Best cheap card: 550 Ti
Best Value: 560 Ti OR 480
If it was me, I would go with the 560 Ti because it is a great all around card. The 480 also provides lots of horse power for the price but it would be my second pick. The 550 Ti is probably the best value gaming card you can get (well maybe the 7770). But only get that if you have to because if you can spend a little more, you have lots more options.