I've been working with the 32 bit ARM chips lately, particularly the "thumb" sized system on a chip ones. You can switch to a 16 bit instruction set for speed and space, but still do 32 bit operations (including floating point). This is the same chip that's in your GameBoy, PDA, car and lots of other embedded devices.
I'm hoping FIRST will switch to these eventually, as they are much more powerful than a PIC. A lot more RAM and FLASH to work with. A tad bit more expensive, but the GNU ARM compiler is free and will host on Windows or Linux. Certainly capable of running embedded Linux if necessary.
I'm thinking FIRST should allow us to choose from a variety of robot controllers, even choose one of our own.
I'm looking at this for my own homegrown robot:
http://www.littlearm.com