Muffler delete w/ straight pipes. $200. Only part of the warranty that is voided is exhaust system from the axle back (since you're leaving the cats stock). Sounds amazing...especially if you like decel popping.
Here's some video:
http://www.camaro5.com/forums/showpo...ostcount=10802
If you want to hear some other options:
http://www.camaro5.com/forums/showpo...21&postcount=1