Last year, I purchased a $35 Linux computer called the Raspberry Pi. It's an amazing piece of hardware, especially for the price.
It's basically an ARM processor-based computer that comes in a few different models. It has GPIO pins for add-on modules and four USB ports.
Mine is set up to perform temperature logging right now. I've done some other nifty experiments with it in the past, too, including some ham radio stuff.
You can install Android OS on it as well but I prefer to run Raspbian (Debian made for the Raspberry Pi).
If you're interested in tinkering with one, I bought mine here:
Totally worth it.
