If you are in the US I'd go to Newegg.com. They ususally have good pricing and post any mail in rebates. They are also amazing to work with if you have to return the product.
At $200 I would recommend a GTX 460 768MB card. They are new, they are powerful, they are awesome.http://www.newegg.com/Product/Product.aspx?Item=N82E16814125334
On the lower side of your budget I would recommend a 5770 1GB cardhttp://www.newegg.com/Product/Product.aspx?Item=N82E16814102898&cm_re=5770_1gb-_-14-102-898-_-Product
I've listed the cards that I would personally recommend. There are other good models but the GTX460 Gigabyte has an upgraded cooler and a slight overclock. The 5770 Sapphire VaporX has an upgraded cooler and a nice MIR. The GTX460 definitly outperforms the 5770, but the 5770 is still a very capible card. Get what you can afford, but the 460 is deffinitly worth the 200 bones.