Official Counter-Strike Site - Everything you need.
CS-Center - HUGE Counter-Strike site.

Top 10 Counter-Strike Clans - Pop up adds all over the PLACE!

G-man's CS editing site - Tweak your game to make it run faster or look better.

Utilities and Programs
CS Manager - powerful utility for Counter-Strike
FILEPLANET - This is a major site for gaming files.
Counter-Strike Alias Binder (CSAB) - A tool help you bind your keys so you can do things faster.

Other Clans

[U.K.E.F] - General CS clan, currently enrolling members.

KTSA - A UK based clan, have their own server, doing pretty well for themselves.