There's a tape someone gave me a while ago put out by Chris Caracci, a formal navy seal. It's actually several tapes with varying degrees of workouts. The one I used to do was a 45 minute one, which was the least intensive one he had, and required no equipment at all (he did the exercises in the desert to demonstrate that you didn't need a gym). The most intensive tape he had was called the Deathwish which was 2 1/2 hours straight, I can't even watch it without getting dizzy. The one I used is called the Industrial Strength PT. I have to admit there's a lot of macho navy seal stuff he goes on about, but the exercises are very good and definitely intense. You should be able to track it down through a google search (this is my first post here I don't know the rules for or against posting website links).

If you can get past the "fluff", you can get a lot out of this workout.