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.
Damn, it looks like they have increased the price on the launchpad since I picked it up. It's now $10. It comes with two micros though with separate use cases, so you can use the launchpad for prototyping before putting it on a breadboard.
