Tabata Protocol aka. Guerilla Cardio
What it is: Warm up for a 2-4 minutes. For the next 4 minutes do 8 cycles of 20 seconds and 10 seconds, where you go ALL OUT for 20 seconds and slow down for 10. Cool down for the next 2-4 minutes (if you can still move that is).
Step 2: Pick your poison. Sprinting outdoors is probably the best. Elliptical machines and stationary bikes also work well (in that order). Thrusters (howto) are amazing. Pushups, pullups, squats? Good, good and great. Treadmills/Other sissy stuff? Not so much.
Step 3: Warm up. Jump around for a couple of minutes. Make sure you are nice and loose. No need to stretch. DON'T proceed if you have any sort of niggles/tightness.
Step 4: Get crackin'. This takes all of 4 minutes, so give it all u've got. The 5th and 6th cycles are the toughest. Don't give up.
Step 5: Falling flat on the ground, not moving, breathing heavy, puking, swearing loudly are all acceptable post-tabata behaviors.
Step 6: Do this 2-3 times per week for 2 weeks. Curse me now, thank me later :)