These are links I find useful.  You might too.
Most of these links have to do with Dungeons and Dragons or D20 materials.

The big sites
Wizards of the Coast Publishers of Dungeons and Dragons.
EN World The premier DnD/D20 fansite.  This place is awesome.
Realms of Evil The not-premier fansite.  They're cool, in a freaky sort of way.
D20 SRD The "System Reference Document" for D20, which allows anyone to write for Dungeons and Dragons.

Not-as-big sites
The Brood These are the folks I'm working with now.  Great bunch of folks.
RPGnow The best place to find gaming PDF's and actually buy them legally.
Powers that Be: City Council My first book!  It's a complete city council, ready to drop into a Fantasy campaign.
SKEIN SKEIN is my first attempt at an "indie" RPG.