Alright, thanks guys. I'll probably mull it over for a little while longer, but I'm thinking of doing something like a vertical scrolling space shooter. Something really simple, and I guess I can add things to it if time provides for it.
Edit: I need to change the way I think about this sort of stuff. It took less than 2 hours for something as simple as a on-rails space invaders-esque game to become a multi-level ship-based action game with upgrades and all that bullstuff. I need to just buckle down this weekend and make some bullstuff and stop hyping stuff up in my own head.