EVGA 01G-P3-1561-KR GeForce GTX 560 Ti FPB (Fermi) 1GB 256-bit GDDR5 http://www.newegg.com/Product/Product.aspx?Item=N82E16814130623
I know its Evga but they are a good company and they do have exceptional warrenty coverage. This card is a little bit over your budget but it does have a rebate and the spec's are good.
EVGA SuperClocked 01G-P3-1563-AR GeForce GTX 560 Ti (Fermi) 1GB 256-bit GDDR5 http://www.newegg.com/Product/Product.aspx?Item=N82E16814130610
This is also nice it costs more up front but has a bigger rebate to bring the cost down to the same as the other one but with higher spec's.
Your power supply is fine and the pci-e express 2.0 is the better technology so you might not utilize the full potential of the card with your MB.