Roborodentia 2009 rules from the IEEE Computer Society - official rules

Robot Resources

RobotMarketplace - motors, speed controllers, gears
Sparkfun - all kinds of development boards and sensors
Pololu - good for all kinds of robot parts
Solarbotics - more robot parts
Electronic Goldmine - surplus parts, very good prices
Budget Robotics - robot parts including modified servos
Jameco - electronic parts store
Mouser - electronic parts store
Digikey - electronic parts store
All Electronics - good surplus electronics store
Small Parts - various raw materials, fittings, connectors
Robot Store - a robot website run by Jameco
Surplus Center - random hardware

You can use a modified R/C servo for a drive motor.  Using a servo can eliminate the need for an H-bridge.  You only need to send a 1-2 ms pulse from a digital output to control the servo.  There are many webpages on how to modify an R/C servo.  Here is one link.