Ok well I happen to have parts from a past failed computer building experiment lying around my house and I need a use for them. I've decided to take another crack at building my own system and as long as I don't get shipped anymore broken motherboards all should be well. The equipment I currently have is:
You've already got a good enough CPU and a great GPU + power supply (I have the same; it can handle my i7 + 2xGTX 470s).
Any of the AM3 motherboards out there will work, but make sure to get one that has DDR3 RAM support (some of the older ones do DDR2; not common, but they are out there), and then you can get some hardy low-latency RAM like G. Skill: http://www.newegg.com/Product/Product.aspx?Item=N82E168...
If you really wanted to, you could upgrade the CPU to a Phenom II X4 955 (one of the best budget gaming CPUs), or throw in another 5770 in CF. They are by no means necessary though.