Longtubes for the 4.0 are sort of limited. Pretty much just Pacesetters, MAC's, and Kook's. The Pacesetters are supposed to be crappy quality, the MAC's are sort of hard to come by, and the Kook's are expensive (but highest quality, probably). There's a company called OBX that sells some on eBay. They're sort of well-known in the import scene from what I've heard. I'm still considering long tubes for the future, but I have a lot of other stuff to do first. I've heard some that sound really good, but that was with some extensive engine modification and a certain exhaust setup. Otherwise, they seem to get sort of raspy on our cars.
2006 Performance White GT 5 Speed - K&N CAI, Magnaflow catback