DIY Cray Supercomputer
I suppose this isn't really an embedded system per se, but since I do write about FPGA-based CPU design here, I thought you might enjoy a peek at Chrs Fenton's homebrew Cray-1. It is 1/10th scale and cycle accurate.
I'm envious! The design takes a Spartan 3E 1600. Unfortunately, I don't have anything bigger than a 1000 so I haven't been able to try it. I can't help but wonder if he's going to fake up a watercooling system for it.