Scott and Cory of Dynamics of Motion demonstrate their 4-minute workout. The basic idea behind it is that instead of stretching out a lower intensity workout over the course of 30-40 minutes, you workout as hard as possible for just 4.
The best part about it is that you don’t need any equipment!
Definitely give this a shot, and check out their book Four Minute Fat Blaster at dynamicsofmotion.com.