http://www.arduino.cc/

A project from Interaction Design Ivrea; lots of boards in circulation at art&technology programs like NYU's ITP program.

Ancestors are the Wiring board and the AVRMini.

Pros:

• Cheap!
• Fast to get up and running
• Cross platform: PC and Mac

Cons:

• Small amount of memory on chip for your programs
• You have to roll your own serial to PC communications protocol

Available in the US via Sparkfun