What's a good, quick, daily workout for a busy college student?

School has started and I fear that I’m already starting to get a bit flabby. I started falling out of shape over the summer, because the last month or two was mostly sedentary for me, and school being in session isn’t going to make that any better.

My schedule is extremely busy, I’m a lazy-ass, and I’m usually sequestered to my suite studying, reading, or tutoring.

I have been doing my best to eat better, but it’s not enough. I want to cut down on my body fat content, tone up my abs, and develop more stamina/endurance.

Any workout suggestions for someone with a schedule like mine?