I've just fired up a Raspberry Pi to get readings from a light sensor via its GPIO port. I'm not an electronics person at all but the Pi is attractive as it is strongly oriented around Python programming.
The eventual goal is to send triggers to the Pi from a computer running PsychoPy via network messages, and use the Raspberry Pi for the hardware interfacing. The goal is to get some validation of synchronisation of various events (visual and auditory stimulus onsets and network messages). Not sure how it will go performance-wise, but being a computer in itself, and being able to communicate over the network, platform and hardware compatibility issues should tend to disappear.
There is something very cool in a lo-fi kind of way in seeing a computer directly responding to changes in the world: