I got one of Kolak's exhausts for my Jeep Grand Cherokee 5.2L ZJ a while back. It was inexpensive but one of the best sounding exhausts I've ever heard. I ended up selling my ZJ since I got a JK but man, I miss that exhaust! Kolak was also easy to get a hold of and the whole process was smooth.
I just hope he someday makes an exhaust for the JK