Manufacturers

Analog Devices Inc. - Amplifiers, Converters, RF/IF Components, MEMS, DSP

CUI - Power supplies, power connectors, etc

Molex - The great connector company

Nordic Semiconductors - ISM Band(s) Transmitters and Transceivers

Samtec - USA based mfg of connectors and cables. They have the wacky stuff for reasonable prices.

Microchip - Microcontrollers - the great PIC family of microcontrollers
 * unofficial PICList discussion forums
 * official Microchip discussion forums

Atmel - Flash memory, ARM microcontrollers, - and the famous AVR microcontrollers
 * unofficial Atmel AVR discussion forums

STMicroelectronics - http://www.st.com/

Cypress
 * unofficial Cypress discussion forums
 * official Cypress discussion forums: start at http://cypress.com/, then choose "Design", "Discussion".

Philips -- many things, including ARM microcontrollers
 * lpc2000 Discussion Group
 * Spark Fun Electronics Forum -> Everything ARM and LPC

If you want information *about* a particular part, the best place is the datasheet -- usually on the manufacturer's web site.

If you want the actual part itself, though -- sometimes you can get samples directly from the manufacturer. But that's pretty hit-or-miss. Your best bet is through some distributor or supplier.

(A "distributor" and a "supplier" are the same thing, right?)