There are plenty of good sites on the web. Here are our collection of useful links:

Forums and Blogs

Allaboutcircuits forum
Edaboard
EEWeb
Epanorama.net 
Maker.pro

Catalogs and distributors

Arrow Electronics
Digikey
Garret Electronics
Future Electronics
Jameco
Mouser electronics
MPJA - Power supplies, LCD, Fans, etc.
Powell Electronics
Sager

Components manufacturers

Altera
AMD
Analog Devices
Atmel
Cirrus Logic
Connect One-embedded Internet chips, modems and Internet fax appliances
Diodes Inc
Epson Electronics America
Fairchild Semiconductor
Hitachi Semiconductor
Integrated Device Technology
Intel
Intersil
International Rectifier
Linear Technology
Maxim
Microchip
Microsemi
Mini-Circuits
Micrel
Murata Manufacturing Co. 
NJR
ON Semiconductor
Panasonic
Philips Semiconductors(NXP)
ROHM
Seiko Instruments
ST Microelectronics
Siemens AG
Silicon Labs
SST 
Vishay
Texas Instruments
Toko
Toshiba
ZiLOG

Passive components

Bomar Crystal & Clock Oscillators
Bourns
Citizen Crystals and Oscillators
Coilcraft
Datatronics
Delevan Inductors
Fox Electronics
Prem Magnetics Incorporated
Rakon high performance crystals, oscillators

RF components

Hamtronics, Inc.
Hittite(Analog Devices) 
Lemos - Low Power Radio Wireless Data Links
Linx Technologies
M/a-COM
Micrel Semiconductors 
OKW Electronics
Renaissance Electronics Corporation RF Micro Devices
RF monolytics AM modules(Murata)
Temex
TTE Americas Filter Specialist
ZComm