Here are links to my favorite D&D web sites:
Order of the Stick
A web comic with stick figures, I have all the printed books and I still can't get enough of this comic.
It has great characters, story, humor all combined into one.
A web comic featuring goblins as protagonists instead of the level 1 opponents they usually are.
DM of the Rings
This web comic starts from "What if Lord of the Rings was a D&D campaign?" and is one of the funniest web comics I ever read.
Dungeons & Dragons
The official web site of D&D. The forums here are great, for DMs and players.
I discovered this web site when I was running Keep on the Shadowfell.
He wrote a series of articles on how to improve that campaign.
Since then I've been a great fan of his writing.
I discovered this web site when I was looking for DM tips.
Each DM tip of his should be in the Dungeon Master's Guide.
This web site has an enormous amount of DM tips, campaigns, preparation, etc.
Each topic is treated in great detail.
I love this web site for its content about sexism and gender roles in D&D.
RPG Blog Alliance
I'm a member of this group and I'm grateful for their support.