I'm surprised no one's replied with "use the search button."
Are you looking for a full system or just a catback?
The most popular seems to be Capristo, but it costs an arm and a leg.
The other ones are Remus, Borla, Fabspeed, AWE Tuning, Agency Power, SpeedArt, PSE, etc.
I'm personally saving for a Remus. Although I haven't heard how it sounds like in person, I've seen vids online and it sounds good to me.
Keep us posted on what you get.