Electronics related forums and mailing lists

General Electronics Forums and mailing lists

EEVBlog forum
4HV - High voltage, Tesla Coils and other danger-oriented electrical things
Stack Exchange Electronics
neonixie - Nixie tubes and other vintage display technology (Google Group)
EEWEB
edaboard.com
The volt-nuts Archives
The time-nuts Archives
computer repair
Switching Power Converters - Power electronics

Company & product specific forums and mailing lists

Online stores

Adafruit
Freetronics
Sparkfun

Test equipment

Agilent Test & Measurement
Velleman
Fluke Test & Measurement

Semiconductors and microcontrollers

Texas Instruments
Piclist - Long-running PIC oriented mailing list
AVRfreaks forum - Atmel microcontrollers
LPC2000 - NXP LPC ARM microcontrollers (Yahoo! Groups)
Xilinx Forum - Xilinx FPGAs and CPLDs
Altera Forum - Altera FPGAs and CPLDs

CAD/EDA software

PCAD - (Yahoo! Groups)