If you just have 1 1080p monitor or less, get a single gtx 670 (680 is a waste of cash) (I have this one
http://www.newegg.com/Product/Product.aspx?Item=N82E16814125423)
You can run every game at ultra at 60+ fps with this card. You would have to get a 800 watt psu to run sli 670.