MBED is pretty cool, nice easy to program ARM (Cortex-M3 mostly) parts, but it used to be a little pricey, I thought. I have an MBED board and it's put to good use, but I wouldn't want to buy 10 of them.
MBED just announced all their stuff is now open-source, and freely useable under the Apache 2 license. Which means you can use the code for commercial products, you don't need to release your code, etc. Very nice.http://mbed.org/blog/entry/mbed-SDK-is-now-Open-Source/
So now we can build our own cheap boards, and use all the MBED code on them, however we see fit. I'm planning on trying it out.