i would just go and get a full catback exhaust system like the ones mentioned above. i would favor the APexi N1 exhaust becuase it has a loud DEEP sound. The Apexi N1 would cost about $450. The exhaust that i have on my car is from TSUDO and it's also an N1 style like the Apexi. it looks exactly like it and sounds EXACTLY like the Apexi N1. I paid about $250 bucks for it shipped. u can get it on ebay for about the same price. it's very good quality too! higly recommend
i wouldnt get a muffler and weld it onto your stock piping. Most of them have an annoying high pitched sound to it. i hate seeing civics rolling around with those fart cans..