Since I don't do research on components, and you didn't give the power requirements of your rig. . .
As big as you can afford. Really. At least a 500 watt or more. With power supplys, more is better. It doesn't work as hard, there's always a reserve, and it will actually use less electricity than a smaller unit.
Building a new rig. Could anybody please recommend a PSU. Will be running a XFX GTX280 xxx edition. intel quad core 3.2GHz processor.
3 2 7200rpm HDD running in raid0.