I know I've said this a million times here but the PYPES brand stainless straight through mufflers are only $75 each and didn't slow my 9 second Dart down at all.
I also ran an X-pipe and Magnaflows on my 9 second DartSport and didn't slow down, even with a 75 pound exhaust system.

The Ultraflows are nice too, and so are the Dynatech split flows.

I have my one chamber flowmasters for sale on my current car(now DIRT cheap if you PM me) because they are way too loud for me on a street car.