I am looking to get together a good list of suppliers for H-Bridges and motor controllers. So far I have found these ones:
Solutions-Cubed Simple-Bridge. This one is pretty good, and its not too expensive. It is an off-the shelf board that includes a controller chip and an h-bridge. It can function from 6-24V for DC brush motors at up to 6A.
Stacking H-Bridges – Make a higher amperage controller out of two smaller ones. This site also has links to 1A and 3A h-bridges
Motor Controller Boards from Pololu
Pololu H-Bridges – L298