falling in under $200 this is what I would be looking at
www.newegg.com/Product/Product.aspx?Item...11&IsVirtualParent=1
www.newegg.com/Product/Product.aspx?Item=N82E16814130826
Both will perform well and they both come with a free game. The EVGA card will have the step up program if you want more power soon after, and it is cheaper after that rebate.
If you end up with any more than $200 there are always better options, but these are the best cards that stay in that budget completely.
There is still a chance that you might end up CPU limited in just a few games, but the better GPU will help you a lot.
Also how are you getting 6 gigs of ram? Thats an odd number for a dual channel motherboard