Digilent ChipKit Uno32
From Hamsterworks Wiki!
The Digilent ChipKit Uno32 looks like a Arduino, works like an Arduino, but is actually a full 32 bit MIPS CPU.
It has a lot more of everything. 128K of Flash vs 32K, 16K RAM vs 2K, more digital and analogue I/O pins - but you have to remember that you are now on a 32 bit chip, so some of those numbers are a bit misleading. Interestingly enough, it is also cheaper than a genuine UNO.
The software environment feels like Arduino (it is actually a modified copy of it), unlike the more 'professional' Eclipse based IDE that similar speced Stellaris LaunchPad uses.
Most, but not all, of the Arduino libraries have been ported to the MIPS code, and any code that requires exact timing or accesses the MCU's resources directly won't work without porting.
Oh, and it is a 3.3V only part.