My vote would be a X1900XT, or XTX if you want the bragging rights. My X1900XTX rig keeps up with my SLI 7800GTX rig in a lot of thing except benchmark scores. For the price a X1900XT is great bang for the buck. Just my two cents mate.
P.S. Oblivion runs nicely after some tweaks on my X1900XTX rig.