A GTX460 requires a 450w psu with 24a on the 12v rails.
The OC does not matter much, the graphics card is the driver of your psu needs.
If you look for a 450w unit or better from Seasonic, Antec, Corsair, PC P&C, or XFX you will get a quality unit that satisfies your requirement.
One should cost about $70, and the extra $10 is well worth it to get quality.
The XFX 650w unit will power any single card made today, and is a bargain at $65 after rebate:http://www.newegg.com/Product/Product.aspx?Item=N82E16817207002