BMW E63 Borla Cat-Back Exhausts 

We have been selling Borla exhausts for BMWs for over 10 years and it is still our Number 1 choice for a cat-back exhaust. Borla designs their exhausts to be not too loud (you don't own a Camaro) and not too quiet (you don't want to drive a hearse either) but rather in the middle. If you're driving with the windows up and the radio on you probably won't hear the great sound. Borla also builds their exhausts from T-304 stainless steel (inside and outside). This means long life (a 1,000,000 mile warranty is part of the deal) and light weight. Comparisons between a stock E36 M3 muffler and the Borla revealed the Borla system is 26lbs lighter!