I like the Magnaflow 4" double walled tips.
4” Magnaflow tips (#35121)
Call JDP Motorsports (vendor on the site) and you'll get the best price around. Check with other people and then check with JDP and you'll see. Don't go by the website prices.....call him and let them know you are with Camaro5.
http://www.camaro5.com/forums/showthread.php?t=64964