You can probably run that setup without any overclocking with a good 550W PSU, but I would definitely recommend at least a 650W one, especially if you plan on using SLI. IF you think SLI is definitely in your future, it might be worth bumping up to a 750W.
As for brands, Corsair and Seasonic are at the top of the industry, and Antec and and XFX have excellent offerings as well. Coolermaster does have some good units, but they can be hit or miss sometimes. OCZ is a decent second tier brand, but only look to them if money is getting really tight.