Arduino powered 7 seg LED display using Shift Registers - I made it at TechShop
Perfboard Hackduino ($8 Arduino-compatible circuit)
Cassette Tape MP3 Player
Halo Covenant energy Sword
The Ultimate Audio Converter
RainBoard - RGB LED Rainbow Fader
Control a Arduino with your phone.
Ard-e: The robot with an Arduino as a brain
Bluetooth your iRobot Roomba!
bouncy sugru bumper for iPhone 4 and iPhone 4S + NEW VIDEO
Wii Nunchuck as general purpose controller via Arduino board
Bluetooth Robot... Fast, cheap and reusable