I have a titanium scorpian racing exhaust(came with bike, but the only other scorpion I can find for it is a carbon fiber one retailing at like 520) and it has a real nice deep throat sound for a sports bike. I have had about a million compliments on it from other riders, usually the first thing they say is that they heard me a mile away, and I was only at about 3000 RPM looking for their house :P

 

This is old, but I still wanted to weigh in with my recommendation of Two Brothers. Amazing sound.