If you can get the 7950 its a great card at stock and its even greater OC'ed. If you can't get the 7950 then the 7870 is also a good choice so long as its the XT version. I'm not sure if Asus has a XT 7870 so I can't give good advice on that card, but you can't go wrong with the 7950.
Why not look into the Sapphire 7870 Ghz edition. I have a pc running 2 of them in crossfire and I love that gpu! You can frequently find that gpu on newegg for less than 200, it comes with some free games, and if you don't mind lightly used, you can snag one on Ebay for 175!!