RS-R is damn nice and is pretty quiet too. My friend has one on his CRX and it's hardly noticable except at wot.

Or you could do like I did and have a exhaust shop custom bend and weld you up something. I've got the dc sports 4-2-1 and 2 inch cat back with a dynomax muffler. It looks almost stock and is only a bit quieter than my friends RS-R.