Ideas...
1. Racing Game (Collision detection would be the biggest issue)
2. Boxing Game (Again, collision detection and timing)
3. Collection of Minigames put together
- This would probably be the easiest to work on, as we could each do a minigame and then share
4. FPS (i personally think these are overated)
5. RPG (Awesome, but restricts the gameplay usually to the storyline, if any)
6. RPG (without storyline)
7. Space Battles
8. Puzzle (probably would have to go with Minigames, unless it was big)
9. Half movie, Half Game (Your actions in the game affect the movie clips)
10. Anything Strategic (that i have not mentioned)
And those are just a few of my ideas =)