Many people use thermoelectric modules, commonly called Peltier modules, to make small things colder.
(Compressor-based air conditioners and refrigerators and freezers are often more practical for cooling larger things).
Both radio and optical astronomy seems to work better when the receiver is cold.
- "Open Source Thermal Cycler" Polymerase Chain Reaction (PCR) uses the Peltier for both heating *and* cooling.
- Another Peltier fridge project: "How to build your own dirt cheap fridge" ("My most important consideration is that it can be service-able by me") 
When a Peltier element is attached to a voltage source, it pumps heat energy from one side to the other, making one side colder and one side hotter. In principle you could use a Peltier element just for heating ( see  )
Typically Peltier projects use a 1-wire digital thermometer or a thermistor to measure the temperature at the important parts, and
FIXME: maybe say a few more words about heatsinks, such as the (open-source?) PowerPeg Thermal Management System ?