fpga in my case is mainly for fun, but I wont refuse to try a cuda/opencl graphics card either. I'm using about 600 Watt on average to keep a building frost-free at the moment..
As I read in a few threads here, the usage of GPU's isn't totally problem free either, or?
One HD5970 need 300 Watt. Put one computer with 2 HD5970 in your building and you have 600 Watt. I don't know if the windows driver support 2 HD5970 at the same time, but linux should do this. Of course you need Internet connection in your building. You need the standard bitcoin client and m0mchil (or puddinpops) miner.
http://bitcointalk.org/index.php?topic=1334.0;all