At the UAC Compound you can check out a new 'openwad' project:
I have a new project for all you Doomers out there. I have made a wadfile for Doom2 that is unfinished and i have thought of offering it to the Doom community for you to complete any way you see fit. The map is for Vanilla Doom so any modifications must also be for Vanilla Doom2.exe... If you make any modifications to this level, when you have finished your version, send me a copy. I would love to see what you have done. If a modification is really good, then i will post it on my downloads page! So get cracking and see your name in HTML!
So get over there and grab the stuff and have some fun.