Aerobics! (of course)
hi-lo- on the floor is my fav, we get jammin & flying around the room, lotta fun!
I also like rollerblading & sprint intervals.
Boxing is awesome too... but I know it's more anaerobic intervals, we run sprints too in the circuit class, so I sorta count it as cardio.
Out dancing to disco is some awesome cardio too!
Anything but biking, ick!