The AVA's interactive group is an informal group that meets each month to discuss interactive art using Arduino microprocessors and other methods of adding interactivity.
Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware and software. It's intended for artists, designers, hobbyists, and anyone interested in creating interactive objects or environments.
Arduino can sense the environment by receiving input from a variety of sensors and can affect its surroundings by controlling lights, motors, and other actuators. The microcontroller on the board is programmed using the Arduino programming language and the Arduino development environment (based on Processing). Arduino projects can be stand-alone or they can communicate with software on running on a computer (e.g. Flash, Processing, MaxMSP). The boards can be built by hand or purchased preassembled; the software can be downloaded for free.
You can get started messing around interactivity for under $50. See the link list below for some of the AVA Interative favorite resources and vendors.