I drove around for about 4-5 weeks with NO muffler on my car. It sounded bad-ass, even tho it is only the li'l d15b2, but it still sounded great. Any of those cheaper bee-can style mufflers should be plenty loud. You could buy a glass-pack type muffler too...those have very little noise deadening design to them.
I noticed I really drove the shit out of the car with no muffler on it tho.