There's a whole host of different aftermarket exhausts to chose from; Miltek, Magnex, Piper, Dreamscience, Mountune etc. etc. Be best to ask around the owners club forum for opinions from people who have each type or who have had more than one type.
Mines still standard at the minute, and I haven't decided to decat it or save up for a race cat, or which company to go with first.