First, who cares what colleges like? Do it because you have something to offer- or you want to learn- not because it's going to help you look good on paper.
As you're working on your idea, I would take these factors into consideration:
- What kind of facilities does your school have, and what can you get access to? Instruments, AV gear, etc.
- What can you get people to show up for? The subject should have broad enough appeal to get at least a few people interested.
- What are your personal resources? What (and who, where appropriate) do you know, own, can borrow?
- A high level of motivation is important- build it around something you're interested in.
- Some general categories of subjects: a) listening/reading/writing/composing, b) playing music, c) audio/video recording, sequencing.
OK, that should get you started- I have my own project to work on.