I am also some what new to this and am also building a new system. I decided to go with the gigabyte 670 windforce OC version. It out performs the 680 for a good 100 dollars less. Regardless, from what I am reading you will need at least a 550w system for the 670 cards, however, I am getting a factory OC version so it may use more juice. I decided to go with a 630w power supply 500 seems to low, though, any more informed insight on this would be great as I would be able to save a few bucks here XD.
P.S. I also can't help but wonder why you are spending so much on your motherboard if you don't plan to sli in the future? From what I have read the asrock z77 extreme4 is really highly rated for a few dollars less. I went with the asrock z77 pro3; I do plan to sli, but since the main game I'll be playing is WoW, not for a long time. From what I can tell our wants are similar, as we have a few things in common in our build, 8 gigs of ram, gtx 670, and the i5 3570k. I have been looking for some insight on the whole mobo/psu situation for a few days in anticipation of my purchase, but what I have read lead me to the conclusion that I would need at least a 550w psu and a mobo that supports my cpu (z77) and pci express 3.0 for the card (gigabyte windforce 670); the asrock z77 pro3 and the asrock z77 extreme4 both meet this requirement.