Better for the environment
The metals, chemicals, and polymers used in producing electronic circuits, as well as the energy consumed in producing them and the extraction (mining) processes can have significant environmental impact. The purpose of this section is to collect information that can be used to assess and/or mitigate the environmental impact. It may also suggest some projects which can be environmentally beneficial. [Note: techniques was the closest major section to incorporate this into but it might make more sens to promote this section to a fifth major section]
Energy Use, Global Warming Gasses
With the climate change crisis and peak oil, energy consumption becomes an important issue. Embodied CO2 includes the effects of emboddied energy plus other CO2 sources. An good source for information on how much energy is consumed and CO2 produced in making a variety of materials is the ICE  database. You have to request a free copy be sent via email. The production of metals and plastics releases many times their weight in greenhouse gases.
Energy consumption by Electronic Devices
Standby modes, switching supplies, etc.
Raw materials, electronic components, bare PCBs, finished products, and end-of-life products being recycled get transported very long distances.
Electronics as energy saving devices
Some electronics are used to save energy. Fluorescent ballasts, Photovoltaics, power inverters, charge controllers, some motor controls, solar trackers, LED lighting, setback thermostats, motion sensor controls and timers, blind controllers, etc. In some cases, computers are used for telecommuting.
The transition to RoHS/lead-free processes has cost the industry a large amount of money and creates problems for hobbyists. When you consider the environmental impact of lead free solders (for example, silver mining is highly polluting), and the greater amount of non-renewable resources used, and the shorter lifespan of the electronic circuits, the whole lead free movement may be yet another political boondoggle. 
John Barnes, electronics text book author, and author of the Pushback site:
It is widely accepted in the Engineering community that the recent ban of lead in solders for use in electronics in Europe is not only erroneous, but will actually lead to a worsening situation on the environment with the replacements being in general use from July '06 having a GREATER environmental impact. 
To date I have collected over 230 books and well over 11,100 other documents on these and closely-related subjects, going clear back to 1851. My collection now fills one-and-a-half bookcases and three 5-drawer file cabinets. 
Based on my research, and helping clients develop RoHS-compliant electronic products, I believe that: If you buy a lead-free RoHS-compliant electronic device-- and if it works when you first turn it on-- it should be safe and fully-functional for at least one year. If you are lucky, it may last a couple of years longer... versus the 20+ years use that we can easily get out of many lead-based electronic products. 
A huge problem with the RoHS laws is the sheer nitpicky nature of the regulations and the beaurocracy that enforces them. It doesn't matter if you reduce the lead content a thousand fold relative to a lead solder board, which would put it well within the 0.1% lead limit. The product is reduced to homogeneous parts each one of which must individually meet the regulations. One stray microscopic lead solder ball might be ok if it is absorbed into a joint where it is becomes part of a larger homogeneous component but not if it contaminates an inspection sticker or gets trapped in the flux between traces. Maybe widespread competent recycling of electronics is a better approach. Not shipping it off to other countries or using prison labor to disassemble it under unsafe and environmentally harmful ways; there are some horror stories of how electronics is recycled now.
Mixing lead containing and lead free components
Many lead-free components are compatible with lead solder processes. leadframe based components, such as QFPs, SOICs, and SOPs with gull wing leads, are generally compatible since the finish on the part leads contributes a small amount of material to the finished joint. However, components such as BGAs which come with lead-free solder balls are not compatible with lead processes.  Also, leadless parts are exposed to higher stresses and are more susceptible to any affect from mixed metallurgy. Check with each manufacturer as lead finishes may vary.
Materials, Chemicals, and Processes used
Ferric Chloride poured down the drain will eat pipes and copper is toxic. Although your sewage plant may not be happy about ferric chloride in the sewage (and it may be illegal) , they can probably at least deal with it better than many other chemicals since Ferric Chloride is used at sewage treatment plants to remove copper. Ferric Chloride etchant can be neutralized into iron oxide (rust), copper, and salt by using iron (nails, etc) to use up all the etchant and then add washing soda and evaporating and can then be landfilled. Considering the value and toxicity of copper, it would be nice to see this improved on so that the copper can be reclaimed.
Etching can be improved, and the lifetime of the etchant before it needs disposal, using citric acid 
See RoHS/lead free section above. Solder paste should be refrigerated (embodied energy) and has a limited lifetime. One problem with expired solder is absorbed water which can lead to spatter and voids in solder joints. What to do with expired solder paste? It should still be ok for manually tinning leads and large copper areas. It may be possible to add it to a wave solder bath using the same alloy.
Tape & Reel, JEDEC matrix trays, other component packaging
JEDEC matrix trays can be reused or recycled. Resistors tend to come in paper (cardboard) tape, which can be recycled, plus a cover tape. Capacitors, transistors, and IC's often come in formed plastic tape with a plastic cover tape..
Hot Air Solder Levelling
Not technically a plating process, but many of the alternatives are. Contains Lead (see RoHS/lead free section).
Solder Mask over Bare Copper (SMOBC)
Sulfur dioxide produced in making copper is equivalent to 1/4 the sulfur dioxide emisions of all industrial nations combined. 1kg of copper requires excavating 127kg of ore and 136kg of other rock and the equivalent of 275 liters of petoleum was consumed.  Copper is somewhat toxic. And it is a scarce and valuable resource. Copper prices are high enough that people steal copper wiring and pipes out of unoccupied buildings (destroying the buildings in the process). Copper can be recovered from PCB etchant by electrolysis.  It also saves on etchant replacement and disposal. They spent 55,000 English Pounds to set it up but it paid for itself in two years. This may be possible to do on a smaller scale. Copper used on printed circuit boards is usually produced by electrodepositing copper onto a rotating drum (Printed Circuits Handbook); this particular process, though often done by the panel manufacturer and not the PCB fab, appears to be compatible with reclaimed copper (no need to remelt it). It appears that electrodes used in the reclamation process can be transfered to the plating bath for panel plating, pattern plating, or making electrodeposited foil sheets, provided the baths are kept well filtered. In a double sided circuit board, most of the copper on the board is electroplated onto the board (starting with a thin foil), thus plating the holes.
"Other concerns we have center on a material necessary for wireless technology, called Tantalum. Tantalum is a rare earth metal that is only found in a few places. Because of growing demand caused by the popularization of cell phone, laptop and wifi use, tantalum mining has become a lucrative business in areas that sometimes have delicate ecosystems and unbalanced economies. This led to wars, exploitation and environmental havoc in the Congo³. That situation has been mostly addressed through policing and international embargoes, but that is just one example of how consumer electronics can be linked directly to environmental and social problems." 
PVC is used as insulation for wires. Flexible Vinyl contains plasticizers which can be toxic and are banned in some countries. Hard Vinyl is safer. There are other plastics, such as LDPE, which do not require plasticizers for flexibility and materials such as silicone rubber which make superior insulation.
Used as a PCB substrate, dialectric, wire insulation, and as a non-stick coating on cookware. Teflon wire releases nerve gas when burned. Teflon cookware (which may be used in the hot plate or toaster oven methods of reflow soldering) is alleged to release nerve gas fumes that will kill pet birds even at normal cooking temperatures.
Silicone Rubber and other Silicones
Silicon is an abundant natural resource. Silicone Rubber has a 50 year life span, which makes it good for durable goods. It is considered by some to be more environmentally benign than many other polymer resins due to its durability, low toxicity, manufacturing process, being chemically inert, and abundant raw materials. Another Silicone, Silicone gel, was vindicated as a cause of health problems associated with breast implants. Silicone rubber is one of the few materials considered safe enough for medical implants. It is an excellent high voltage insulator and withstands high temperatures. When used in contact with electrical circuits, peroxide curing vs. acetic acid (vinegar) curing silicone should be used due to the corrosive nature of acetic acid. Silicone caulk may be thinned to make it suitable for painting or dip coating, when the proper forms of the resin are not available, using Xylene (a hazardous material) or pourable silicones or other silicones without thixotropic additives may be used, though these are expensive in small quantities. Silicone rubber may be used as an adhesive (it must be cut to remove it). It may be used as a potting material. Silicone oil is used as a lubricant; purists prefer pure silicone lubricants (such as CRC 100% silicone) over products such as WD-40 which mix it with petroleum based oils; do not use it on a surface you intent to paint. Paint does not adhere to silicone rubber, either. "Paintable" silicone rubber caulk appears to lack the thixotropic additive and is thin enough to spread with a paint brush, though probably not thin enough for dipping or pouring. Liquid silicone may be used as a non-toxic solvent. Availible in electrically conductive varieties. Silicone is used to make flexible molds and hobby moldmaking suppliers are a source of small quantities of different types of silicone rubbers. Silicone rubber will withstand reflow soldering temperatures; it could be used to adhere components to a board before soldering, however it will not let go when you attempt to desolder the parts. 
Can be used for breadboarding leaded components, enclosures, etc. Low embodied energy/CO2.
Panel Plating vs Pattern Plating
Chemical Etching vs Mechanical Etching
Laser Cutting (stencils, engraving, via hole drilling)
Recycled polyethylene lumber (ReHDPE) (Not the kind with wood fillers), seems to machine well, is cheaper than delrin and other plastics. Wood fillers in the sort found at Lowes Hardware stores may absorb water. At least I think the sample (from teksupply) I saw was ReHDPE; they don't say but similar products seem to be ReHDPE. There may be voids. 2x4 material (many sizes available) is about $3 per foot.    May be useful for electronics enclosures and other plastic parts. HDPE has a lower embodied energy than most plastics.
The enviromental impacts of electronic devices are greatly exacerbated by obsolescence (or worse planned obsolescence), limited lifetimes, and poor repairability (including lack of technical documentation), and by often being cheaper to replace than repair.
Single Function vs. Multifunction devices
Devices which perform many functions, and thus replace many devices, may reduce environmental impact. Do you need a computer, TV, stereo, CD player, DVD player, game console, DVR, VHS/DVD recorder or can you use one device (the computer) for all those functions? Do you need separate PDA, GPS receiver, digital camera, camcorder, cell phone, DECT cordless phone, voice recorder, MP3 player, and ebook reader or can those be combined into a single portable device that functions better than the individual devices?
The embodied energy in a Monocrystalline solar panel, 230Kg CO2/square meter might be a some indication, though that is for the module and not just the cell and it is based on a square meter rather than by weight as most things are, but it seems rather high (they do, however, repay that energy in about 18 months to 7 years). 60% of the embodied energy is in the silicon wafers. Pound for pound, semiconductors are probably an environmental nightmare, though very little material is actually used in the final product. Unfortunately, a 2g chip (32MB DRAM) requires 1.7kg of materials (72g of chemcials, 1600 grams of fossil fuels, and 700 grams of elemental gas) and uses 32000g (32 liters) of water. A lot of this energy is too heat the materials to 1000 degrees Celsius (how about a large concentrating solar collector to help out here?).
The process of making resistors generally involves baking (embodied energy/CO2); probably twice, once to make the ceramic subtrate and once for the resistive coating; however, this is probably not a major concern as ceramics have a fairly low embodied CO2.
Computers have a very large environmental impact and may be indicative of the environmental impact of electronic devices in general. For a computer, the emboddied energy is about twice what it will consume over a three year life span.
For a desktop computer (not counting monitor, etc): 6050g steel, 670g copper, 440g Aluminum, 650g plastics, 1040g Epoxy, 47g Tin, 27g Lead, 18g Nickel, 1.4g Silver, 0.35g gold, and 96 grams misc for a total of 9040g. A 17" CRT monitor: 6817g Glass, 2830g Steel, 700g Copper, 480g Ferrite, 240g Aluminum, 3530g Plastics, 140g Epoxy, 20g Tin, 593g Lead, 1.24g Silver, 0.31g Gold, and 98g of other materials. "Other" is probably largely the fiberglass in the PCBs and the silicon wafers.