Two words. Sub Thump.
This is one of my most favorite modifications. Subthump makes installing a subwoofer system in you car a breeze. It only takes about 30 minutes to wire up with their harness. They also make this custom box that took me well over 2 hours to get in and positioned. (I guess that's kinda a good thing). It was driving me nuts getting it positioned. But at the end my color combo I'm going for was instantly set off.