Absolutely rebounding is a FANTASTIC cardio workout ...
Now here's something to bear in mind -- the average rebounder will allow you to weigh up to 300 pounds (above that you need special ones that often cost a small fortune), and you probably need a "stabilizer" bar (so you don't lose your balance while rebounding).
I've got a short, sweet, to the point write-up on rebounding here:
http://1healthyboomer.com/step1_rs.htm
SharonM