Simon Monk has launched a new robot kit based around the Pi. It includes the following for £55:

• a robot chassis, including two gearmotors, two wheels and a 6 x AA battery holder.
• a RaspiRobot Board v2 (RRB2) that plugs onto the Raspberry Pi and controls the motors, as well as providing power to the Raspberry Pi itself. It uses a switch-mode power supply that can provide the Pi with up to 2A of current. Plenty for a WiFi dongle, display and pretty much anything else that you might want to attach to the Raspberry Pi.
• an HC-SR-04 Ultrasonic rangefinder
• nuts and bolts to hold everything together

You can see more about the kit here