http://www.doomworld.com/doom3d/

this thing has support for it; looks pretty sweet. wonder if it will work with gbdoom?

http://legacy.newdoom.com also supports split screen deathmatch. Never tried it myself.. but in theory I suppose you could do gamepad, and keyboard. Legacy is probably a better port than doom3d. I've also done some test with some of the GL ports out there… zdoomgl is nice.

I tried the splitscreen thing just too see if it worked…too my surprise, it actually did too bad doom3d's not compatible with gbdoom also more than one player can se the keyboard with clever key mapping…I have yet to play against someone though, it should be quite fun indeed.