If you've got to go, go here!
I know there's not much hear yet, but bear with me. :-/

General Doom Sites

Doomworld, Newdoom, Doomcenter
The three biggest Doom news-related sites on the internet. Meet lots of other Doomers on these sites!
Official site for this excellent Doom source port with the best gameplay enhancements of any. Several ports have been built off it, in fact.
Doom Legacy
Official site for another widely-used source port. This one is most often used on Doom Connector, as it does not lag like ZDoom unfortunately does. 
ID Software
 If you don't know about them you must have been buried under a rock for the last ten years. Visit them or die... myep.

Member Sites

Tower of WAR
Official site for this megwad. Read more about it here or at this site's projects page.
Jwarrier's Doom2 Site
Jwarrier's personal site for Doom 2. Has info, downloads, forums, etc.