Like you, I cruise the net looking for things to help improve my campaign, and get a little bit of an edge on my players.
  Here's a few sites I found that can help you out....

Realms of Evil - Good content, good forums
ENWorld - Latest d20 news, reviews, and a pretty big set of forums
Mortality - DM's resource and d20 news.
Wizards of the Coast - The D&D site itself. Now owned by Hasbro
RPGNow - Quality d20 PDF's and downloads, not to mention forums. Check it out, and check the publication I co-wrote: Crimson Contracts: Assassin's Manifesto
Ambient Inc. - My imprinter and publisher. A job you couldn't pay me to do, but I can pay them to do for me!
Wolf's Den - By my co-writer. Good site, lots of 2E stuff. Soon to be updated to 3E


If you want your site placed here, just drop me a line, and I'll put you in.