A lot of the 3.5 guys say that a single in dual out Jones Full Boar muffler sounds great. I put a similar set up on my old 3.6 and it sounded good, loud as heck but I loved it. Most think the 3.5's sound better than the 3.6.
Blastin' Bobs has some great options. Love the one I got for my R/T and will be upgrading this summer to one of their Catback systems. Check out some of their options. Definitely affordable and you won't be disappointed in the sound.