Ok here is my contribution. Flowmaster 40 series no catalytic converter. I chose this combo because it was cheap, I live in Indiana, and I kind of did both on a whim. Sound is pretty raspy with out the catalytic converter. It was much more mellow. I think this video will give you an idea what it sounds like. Right click save as or stream.
I have one on streetfire. Search for 318ti. It won't let me search right now.
http://arcowling.iweb.bsu.edu/snowmovie.mpg and
http://arcowling.iweb.bsu.edu/snowmovienotraction.mpg