Who needs to pay for "Insanity" or one of the other advertised workouts when you can get a great workout in with a regimen like this. The best part about this, you don't need any equipment, just youself and a hard floor...and probably some gym shoes.
The 30x3 Workout
30 Crunch-Togethers (extending your arms straight above your head and your legs out straight, bend you knees and 'crunch' together you upper and lower abs, holding for 1 second)
30 Body-Weight Squats
30 Lung-Jumps (15 each leg)
Then to finish it off...
:30 of Planking (back straight, abs and gluts tight - do this TWICE)
This should take you approx 15 minutes...good luck! You should be a little sore the next day!