Just answered a similar question for someone else and realised how insanely cheap parts are in the U.S. compared the the U.K. You can get a really great build for that price.
Intel Core i5-2500k $219.99
Hitachi 500GB HDD $38.99
EVGA GTX 460 1GB $159.99
Corsair Builder Series 600W $64.99
Corsair XMS3 2x2GB 1600Mhz $49.99
GIGABYTE GA-P67A-UD3-B3 $134.99
HAF 912 $59.99
Windows 7 Home Premium 64 Bit $99.99
Coolermaster Hyper 212+ $29.99
You still have over $40 left there and also $50 in rebates, there are many things you could do with that cash. I'd suggest save it OR get a bigger HDD and better case OR get a x8/x8 SLI ready motherboard with a suitable PSU to get another GTX 460 in future OR get something like a HD 5870 instead of the GTX 460.
If you decide to go with the build i suggested you should know that you will definitely want to OC that GPU and CPU, seems like a waste otherwise because they are pretty underclocked imo.
Yeah pretty sure that one supports x8/x8 crossfire, think that means it will do x8/x8 SLI too but i'd double check that one. If it does then with the extra cash you could get that and a 650-750W PSU and then you could go SLI/crossfire in future.
Take a look at the Intel® Desktop Board DP67BGB3; this board support both SLI and Crossfire in x8/x8 configuration. The DP67BG is one of our extreme boards meaning that it is designed to give you rock solid stability and high-end performance features. If you are willing to step back from the support for SLI and Crossfire you can take a look at the DP67BAB3 board.