This will be a mining-only rig.
Would like to be in the 750M - 1 Ghash range
A budget helps

My friend and I put together a 1.2 GHps rig for about $1100. No case, no hdd/optical. <$1 per MHash is very doable.
5850s, AMD quad, free RAM, and MSI 890FX board with 1 kW PSU. Should work well. Building tonight =)
Lol, I put together a rig for <$500 that will put out almost 800Mhash/s.
Shop around is all I can say. Check lots of forums and websites for good deals.