Here are the ATI recommended power supply requirements for the ATI Radeon HD 5770 and 5750 video cards:
450 Watt or greater power supply with one 75 watt, 6-pin PCI Express® power connector recommended
600 Watt or greater power supply with two 75 watt, 6-pin PCI Express® power connectors for ATI CrossFireX™ technology in dual mode.
The recommendations are for an entire pc system..
Corsair and Seasonic are two brands that have a reputation for high quality power supplies that consistently earn high marks in technical reviews. They are reliable, stable, and come with a 5 year warranty in the USA. Some of the newer models come with a 7 year warranty.
Here is a link to a list of Corsair power supplies and prices at newegg.com:http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=2010090058%2050001459&bop=And&Order=PRICE&PageSize=100