There are a ton of good options, each of which are better than the "official" Audi aftermarket one.

Most exhausts are a minimum 2.5" through, including MTM, Milltek, Neuspeed, APR, AWE, and Borla.<ul><li><a href="http://forums.audiworld.com/southeast/msgs/8155.phtml">http://forums.audiworld.com/southeast/msgs/8155.phtml</a></li></ul>