I would recommend this card:http://www.newegg.com/Product/Product.aspx?Item=N82E16814161454
It is the most powrful card on the market for that price, and it is the latest generation of AMD cards for the price. Unfortunately, there are no cards that will really be able to keep up with your cpu for the price you specified.
Also, your PSU will be on the very edge of acceptable at best. I would highly recommend an upgrade there before a graphics card.