There is something called the NuVinci CVT, which can be used on bikes to provide an UNLIMITED number of gears.  That's pretty amazing.

The NuVinci CVT (Continuously Variable planetary Transmission) system contains balls on the inside that, well... just watch the video, I don't think I'd be able to explain it.

When it's equipped on a bike to change the transmission you have to twist the handlebar to increase/decrease the drive.

This thing can be used on more than just bikes too.  It can also be used on...

• Light Electric Vehicles
• Automobiles
• All Terrain Vehicles
• Lawn Mowers, Golf Carts, etc.
• Agricultural Equipment
• Wind Energy

Link: Fallbrook Technologies