As someone else has already said, exhaust, i would recomend a milltek full system. Its quite expensive but well worth it i think, then for the filter you could either get the pd160 intake and green panel filter or go the dynatwist route which i have done. It doesn't really make much of a difference with the casing on and the cold air feed pipe on but if you take them off and have just the filter exposed then thats a whole different story.

I took mine off today just to see what its like and if you cain it then its a little louder but if you change gear at low revs ie 1.5- 2k it makes an awsome sound. Its like having darth vader under the bonnet lol. But the decision is yours.