A mountain bike with two sets of tires, one for the roads, the other for off roads, will be the most versital. However look long and hard at a Surly Long Haul Trucker (the link is correct but not working for me at the moment). It's a touring bike, that makes for a fantastic commuter.
There will be those who say to only keep a beater in college. It depends on where you go to college, not all are dens of bicycle thieves. Keep a good lock on it, (Sheldon Brown Lock Strategy, good info), and be aware of where you lock it up. I made it through my undergrad degree without a single problem with a nice Cannondale.