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 (Google Group) Nixie tubes and other vintage display technoogy
EEWEB

Company & product specific forums and mailing lists

Online stores

Adafruit
Sparkfun

Test equipment

Agilent Test & Measurement
Velleman

Semiconductors and microcontrollers

Texas Instruments
Piclist Long-running PIC oriented mailing list
AVRfreaks forum Atmel microcontrollers
LPC2000NXP LPC ARM microcontrollers (yahoo groups)

CAD/EDA software

PCAD (yahoo group)