Well, maybe the idea was planted in your mind when I suggested we make an online mode of space marine
IDEAS:
There could be a racing game too, with a couple of simple tracks, maybe some Mario Kart style powerups
And there could be a multiplayer drawing sort of a tool built in too (for when I have epic ideas that can't be put into words)
Maybe a team zombie survival game (green circles come in, shoot them to kill them, if they touch you, you become a zombie)
Hangman? Everyone loves a little hangman.
Interactive musical tool/game thing? Like a piano and you click the keys to make notes, and maybe a drum kit too
Some sort of a fighting game (like SSB, Tekken, Street Fighter, Mortal Kombat, ect.)