I'll put my recommendation in for Insanity
I was skeptical at first, but what helped convince me was the fact that you don't need any equipment. Just some open space and a dvd player. I haven't really followed the food/nutrition guide as it's a little too hardcore for me. I've done the 60 day workout a couple of times and now for maintenance rotate through 3 of the longer/more difficult second month workouts on a weekly basis.
Overall it's helped me lose a bunch of weight and overall I'm more fit than I've probably ever been.
Jeeze, they should be paying me for this. If you're looking to get in better shape and are willing to commit the time (~40 mins/day, 6 days a week for the first month and ~60 mins/6 days for the second) I find it to be well worth the money. Got mine from Amazon.