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. Some of the newer models come with a 7 year warranty. Lately we've been seeing a few other brands offering some high quality units. One example would be the Antec Earthwatts and Antec TruePower New models which are a major improvement over Antec’s older psu’s like the Basiq models.
If you are on a tight budget the Corsair VX450 would be appropriate:http://www.newegg.com/Product/Product.aspx?Item=N82E16817139003
However, if you could afford $10.00 more I would recommend the Corsair VX550. It is a real work horse that can easily power a pc system with any single video card made.http://www.newegg.com/Product/Product.aspx?Item=N82E16817139004