http://www.arduino.cc/
Best of all, it's open source. If only I knew what I was doing, I could build/assemble/code my own devices for all kinds of stuff.
This place has a ton of other goodies for sale.
They have:
USB-based microcontrollers ($35)
GPS receivers
Accelerometers
Ultrasonic Range Finders
Gyrometers
They even have a line of wearable circuit boards that are designed to be sewn into clothing (and they're washable). They have microcontrollers, light sensors, power supplies, buzzers and accelerometers in this style.
Now, I'm not sure whether to go with the embedded device route or the super tiny PC route. The embedded device route would be much cheaper, but I'd have to figure out a whole lot more stuff. Also, with the Arduino embedded system, I'd have to write a lot more software and couldn't use the Enginuity Logger very easily.
