Clicking around, I found this PIC32-based board. It's the same form factor as an Arduino Mega board, but it's powered by a PIC32 running at 80MHz. This is an 80MHz MIPS CPU too (a RISC CPU you'll see all over the place, and is somewhat similar to ARM) that has integrated USB and Ethernet support. Not to mention 512k of flash and 128k of SRAM. That's a lot of horsepower for a little board. And it's only $50, that's not bad at all.