One of my coolio swiss ball exercises atm is (and I hope I can describe this properly)
Kneel on swiss ball-don't sit on your heels etc
Lift arms over your head
Breathe and bend over as far as possible using your quads etc for stability
Lift self back up

To add more excitement, hold a broom stick horizontally whilst doing the above.


Another one using a bosu or 1/2 bosu
Sit on & balance then manouver self back to flat position then bring self back up. I can sort of do it on a swiss ball but keep losing balance at a certain point.