Mingdd, I would get a brand name universal muffler so you have some kind of warranty, it's just safer. Companies like DC Sports or Apexi has a lot of mufflers. You don't have to restrict yourself to what are called Universal Mufflers, Apexi has a whole range of mufflers that have unique looks to them. The size, shape, and material are what will determine the sound of the muffler. It will be nice to have the option of a silencer, too, for when you're driving on the interstate and don't want that continuous droning sound (silencers also add a bit of low end torque at the expense of a lot of top end, so more passing power too). I'm sure your local auto store has some unique mufflers in stock, too. Try Autozone or Advanced Auto Parts, might want to call them up just to check so you can see them in person.
That's all there is to it, just find a muffler of which you like the look. We can't help you with that.