I have a 550W Antec Neo HE. It runs my eVGA Superclocked GTX 280 just fine. This power supply has a combined amperage of 42A (504W/12V) across all three 12V rails which is slightly above the recommended 40A for a single card. This is my current rig specs.
The card is overclocked to 700/1400/2400 and everything runs perfectly fine. I've looped 3DMark demos for 14 hours straight at these speeds without a single problem.