Skipping
 

For some kick arse cardio work, go buy a skipping rope. Ive been combining it into my training every so often, and it really gets you very fit, and sore. Its also great for your footwork if you play a sport or dance or whatever.
In addition to this, you can workout different parts with the rope depending on how you do it eg, raising your knees hammers your stomach muscles.

I should dig my rope out. I started skipping rope a while back, but was soon discouraged. Now that I'm in a bit better shape...sounds like fun.

Thanks for the tip.

Also, if you're involved in a sport like basketball or volleyball where jumping is critical, skipping is one of the best things you can do for your vertical.