Dynomax, MagnaFlow, Flowmaster have all been recomended here.
You need more than just a muffler though.
A full 2.25" cat-back exhaust with high flow cat, no resonator, and a muffler will release a good amount of power.
Of course there is always the option of getting a SVT exhaust put on your car.
Expect less than a 10HP gain from your CTA intake.
It produces a very nice sound when accelerating.
