I recommend the Supersprint exhaust for all non-M3 e36 cars. Just make sure to get the 325/328 exhaust. The tips are rolled chrome with supersprint logo engraved. It's got a deep hum that isn't very loud. One of the quietest performance exhausts, only loud below 2500-3000, a bit of droning, especially when the exhaust is hot.. sets off car alarms easily in that state.. or it's loud when you go WOT. In my opinion, the best looking tips. If the picture came out clearly I'd post it, but compared to a soda can, the SS tip diameter is about 0.5 inches larger.. and It's the exhaust I've got. $500-$550 shipped for a good price. Check supporting bmw forum vendors for those prices, otherwise it'll be $550-$600 + shipping
My second recommendation would be the Active Autoworks exhaust. It's one step up in terms of loudness next to the SS exhaust. It sounds great, although not as deep as the SS. It's got a higher pitched Ferarri sounding note. But I do like the way this one sounds though! Only problem with this one, like many other performance exhausts, is that there's only an M3 version that fits non-M3's. THe problem with that is that the tips stick out a little further because the M3's rear sticks out further. THe second problem is that the piping for the M3 exhausts are larger, so you will lose a little power on the low end. $600-$650 shipped, pretty much anywhere.
As for that test posted above, keep in mind that's for an e36 M3. Numbers for a non m3 e36 will be different with the AA exhaust. Actually, I bought my exhaust from those guys and they recommended the SS for my 328is over the AA because the AA #'s would be lower since it's designed for an M3, but SS has exhausts for all BMW applications...