Nakedman's TC List is
a comprehensive listing of all the TC's and PC's there are, and a TC news source.
The TC Magazine occasionally
regular reviews of TC's and PC's as well as a conversion news listing.
Here's other links that are just general good Quake sites..
News related sites
Planetquake
Blues News
sCary's Shuga Shack
Redwood's
Other sites
Slipgate Central
The Quake
Modeling Association.