Another option is the Eisenmann quad exhaust for E46 non-Ms. It runs about $900 and has a great sound to it. You can do a search for it but here is how it looks on my ride:
Looks much better in person, I just suck at taking pictures. I get lots of compliments, even from pure BMW enthusiasts who don't like any "form" that doesn't have a "function".
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Ramsen

2000 Black/Black 328ci--All Clear Signals--Painted Reflectors--Kamei eyebrows--MVR front apron--Racing Dynamics Side Skirts--rear windows limo black--blue neon throughout cabin--Blaupunkt DVD player and 7" Koiller lcd--Diablo Racing Burgini 18" chrome wheels with Bridgeston Potenza S-03--Racing Dynamics Front Strut bar--K&N Intake--Quad tipped Eisenmann Exhaust--AA chrome oil cap