Are you only ever planning to use one of them? If so a good 500 or 550W PSU from Antec, Corsair, PC Power & Cooling, Seasonic, or OCZ will do fine. If you are planning on getting 2 look for a 700 or 750W unit from those manufacturers.
All of the manufacturers that i listed make good PSUs and you really cant go wrong with any of them, so pick the one that is the better value. There really is no best among those 5, as they all have very similar units. OCZ now owns PC Power & Cooling, and Seasonic makes the innards of many of those brand's PSUs and they all perform quite well so its hard to figure a best among them in general unless you are comparing specific models from each one.