http://chrisfenton.com/homebrew-cray-1a/
This guy implemented a Cray-1A in a Xilinx Spartan-3E 1600 FPGA development board... and then went and designed a 1/10th scale model case to put it in! I'm a little unsure how he can claim it to be binary compatible and cycle exact when his main problem seems to be that he has no software to run on it, but whatever. The hardware reference manual he links to is very interesting also.
I've always dreamed of owning a Cray, though the logistics of it are completely ridiculous (y'know, like having a 150kW power source for the cooling system, and reinforcing the floor to support a 10,500lb machine and all that fun stuff).
--Zero