I'm a fan of the Magnaflow single in-dual out mufflers. You can get a 2.5" or 3" in, dual 2.25" out that looks reasonably stock-ish and has a pretty mellow exhaust note. A friend of mine had a 3" in-and-out Magnaflow on his old DSM and I really liked the way it sounded. Probably a bit louder on an NA car, but that will be the case with any muffler.