OK, so a single card. suggestions for NVidia? My price range is up to $500 or so. please keep in mind my 30" 2560 x 1600 monitor.
The 7970 GHz Edition card is the best single GPU card out on the market.http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107-7.html.
The only Nvidia card comparable to it is the 680, which the 7970 GHz outperforms the 680 at higher resolutions due to the 3GB of VRAM and the bigger bus. The 7970 GHz edition is my recommendation for your budget. If you are truly set on the Nvidia route, get a 670 as the 680 is not worth the 5% increase in performance for more money.