The MSP430 Family from Texas Instrument is quite young, but it's also a fun series of µC to play with. They're really really cheap, which make them perfect to embed anywhere.

In the arduino-shield-spirit, there are some Boosterpacks that can be plugged on the MSP430 Launchpad, perfect for prototyping.

• Launchpad
• Chronos Watch

• Life: Conway's Game of Life on a 6×7 Charlieplexed LED Matrix
• TLCDrive485: RS485 3W RGB LED controller, with TLC5940 and Max485