I'm running a magnaflow cat back (5x11x22" Muffler, 3" & 4" Tubing, Side Exit, 4" Tip), it sounds very good and it is not that loud, I keep the cats though.
I've also heard that the magnaflow single in and dual out is quieter.

here is a link for the universal mufflers: http://www.magnaflow.com/02product/ss.htm

Hope this helps.