Mufflers
I've got a Flowmaster with a CarSound high-flow cat on my Ram, it sounds awesome.
On my Duster I've got a pair of old Dynomax Bullets, 3" in and out. They sound good, but they slow the car down by almost half a second. I've heard that the Dynomax Ultra mufflers are like running open headers, as far as power is concerned, and they're pretty quiet.
The Bullets I have now are plenty loud, though. Take a ride with me, you can hear how they sound at full throttle:
http://www.burwoodboysracing.com/Movies/May29-Run2.wmv