Depends what you need to fit into that budget besides the main components (cpu, ram, mobo, gfx).
If you only need the main components, get e6600, ds3,asus p5b deluxe or maybe even a 680i or r600 would be good, 2 gigs of good quality 4-4-4-12 ram (the geil is pretty good for that price), and you could maybe even squeeze in a 8800/ refresh depending on when they come out.