Current QuickPoll results for 207 entries:
What's powering the balloon?
Hot babes, ...no need for fossil fuel!
The stars, ....heavenly bodies.
Dawn's fusion reactor, still a few bugs, but enough juice to get off the ground.
Anti-gravity bikinis, ..a gift from the Legion of Super Heroes.
Geek's hot air, ...pant, pant.
(May not add up to exactly 100% due to rounding, and the constant expansion of Cartoon Reality.)