As long as you have the power to push it you can buy whatever your hear desires.
But if simplicity is all you want, a Radeon R7 240 would be about all you really need.
http://www.newegg.com/Product/ProductList.aspx?Submit=Property&Subcategory=48&Description=&Type=&N=100007709&IsNodeId=1&IsPowerSearch=1&srchInDesc=&MinPrice=&MaxPrice=&OEMMark=N&PropertyCodeValue=3055%3A94398&PropertyCodeValue=679%3A446069