500w PSU would put you down to very few watts for future upgrades, not to mention be pushed probably higher than it's efficiency %. Also you don't want to push your PSU to anything over it's efficiency %. So I would recommend a 650w-750w~ PSU for your setup if you want it to be safe/last you a WHILE (even for your next setup).
People often underestimate the need for a good quality power supply with ample wattage room. For example my setup is running under around 350w with full load, my PSU is 400w... I can expect it to last me... 6 months before it dies, however I will probably replace it very soon (next month maybe)....
If you know you will not CrossFire, a Corsair 550VX will work very nicely. If you are considering running two video cards, I'd get a Corsair 750TX - plenty of power and it has the necessary cables to power the video card.
My second choice would be Antecs in the same power class.
I would say a solid 500-600W PSU would be good. I am talking about a newer model that has a good amp rating on the 12v rails. 30A+ or so. That should do you well. If you plan on a 2nd card maybe a 750w. I have a PC Power and Cooling 750w and I like it alot. I can throw a 2nd card in there if I want an and have 60A on a single rail.
Just remember there are 500W PSU's and there are 500W PSU's.. The power supply you listed above, what are the specs on it?