Well, if you are only going to use one video card and don't plan on using mutiple video cards, then a 750 watt power supply is more than sufficient for your needs. The very high quality psu's such as the Corsair TX750 you are looking at is designed for high end systems with two video cards in SLI or CrossFire mode.
If you are positive that you will only be using one video card, then a high quallty 500 watt power supply such as the Antec Earthwatts EA-500 will meet your needs. It can power any single video card made.
Here's a link to a technical review of the Antec EA-500:http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=35