http://www.3fatchicks.com/forum/showthread.php?t=81791
Check out that thread about the rebounder - its a mini trampoline. I jog on mine (2 minutes average speed, 1 minute sprinting) for 35 min - its great for your lymphatic system and really gets the heart pumping and the sweat flying. Plus, its quiet enough that you can watch TV, and its easy on the knees because there is no hard "stop" of hitting the ground like in jogging, you just glide back up because of the elasticity of the trampoline. You can also do jumping jacks on them, or just bounce up and down.
Amanda