1) Scrap the 680. Go for a 770 instead, they are exactly the same graphics card, and the 770s can generally be found for cheaper anyway.
2) Don't get such an expensive sound card, they are generally always not worth the money, and especially PC PCI based sound cards as well (they use cheap parts, put 'em in a fancy shell and sell them for high prices)
3) With the money saved from graphics card and sound card, get a better PSU. Either a 650w for 750w would be plenty, but personally I wouldn't risk a 680/770 with only 500w, especially if you plan to overclock in the slightest.
*edit* Please don't bump, it's being replied to, some people may not even see the thread for a while, if at all.