On my old 98 Gt I ran a Mac 2.5" H-pipe (off road series) to a Flow master American Thunder cat-back system. The car sounded mean and loud. i personally liked it but when I say loud, its loud.

On my current Car I run a hearder back Bassani x-pipe/cat-back system. It's not quite as loud at times but has a nice back rumble to it on decceleration and absoultly screems at WOT. I personally like my Bassani system better but it is quite pricey.