What sort of project are you doing? I just picked up a teensy 3.1 ( https://www.pjrc.com/teensy/teensy31.html ) for a project I'm working on, and it's got a good amount of horsepower. If you don't need a horrible amount of power, there's also the MSP430 boards which start at ~$5, and go up from there. The low end has been covered for a decent amount of time, this board is actually interesting for the upper-end where you need something fairly beefy, but don't want to start looking at rolling your own board.