I currently Have 1 896MB EVGA gtx260 OC edition and can get another on EBay for around 50$. I play games such as WoW, Black ops, Diablo 3, Assassins creed series and some driving games. Would i benefit more for the money by just getting a second card or spending more than twice as much on a higher end newer card? My system and CPU are newer, AMD Phenom Black 6 core and 12 GB ram. Asus MB. Thanks.
Off-hand I'd expect SLI gtx260s to be about in the range of a 470 or 560 ti. For $50 it might be a worthwhile upgrade as long as your mobo and PSU can accommodate it. It's not going to have a lot of longevity, but will give you some extra fps for relatively little.
I upgraded my Gigabyte GTX260 recently, with a Sapphire VaporX HD7950. I had extensively benchmarked the old card, and it turns out the HD7950 is CLEAN 3x as fast as the GTX260 in basically everything (DX9 and 10), and uses LESS power doing it(!). I'd sell the GTX260, and just get a new GPU. Just my opinion of course.