Cytomax (my favorite)
Accelerade Recovery (another favorite)
Hammer Heed
ClifShot Electrolyte
First Endurance EFS
GU Electrolyte Brew
Gatorade, Powerade, etc. all contain too much sugar and are just sports drinks sold as an alternative to soda. I never drink anything but water while on a ride though unless its over 100 miles. I fill a bottle with Cytomax or one of the others for the end of the ride and use them primarily for recovery. I prefer soft solid foods for an energy boost while on the ride.
All are available at your LBS in bulk or single serve packaging or by mail order through
TriSports.com and many others.