Best way to cure rattles are with the upgraded corksport exhaust hangars, and of course aligning your outlets to be centered inside the tips.
Magnaflow, GHL and CP-e are the most popular. GHL's system is pretty neat because it replaces the fake tips (no chance of rattles), looks dang good, and sounds mean as hell.
All the kits are pretty spendy. I had the CP-e dual CBE to match my downpipe (absolutely loved the sound and performance I got from it - well worth the $1,200). Here's a short clip of mine: [video=youtube;Q18yBBoqz7M]http://www.youtube.com/watch?v=Q18yBBoqz7M[/video]
Install was pretty easy. A neat trick to get the hangars loosened is windex. It's a savior. If you're going just for sound, get a cat-back. If you want performance, go turbo-back.