I was trying to find an option that was small and wouldn't give the person in the car next to me a seat massage so I finally decided on the Kenwood KSC-SW10 the link to kenwood's site is here
Kenwood - KSC-SW10
I'm still trying to figure out where I want to put it at though, it doesn't fit under the passenger seat, anyone else have the same thing and have it mounted somewhere?
Overall though, it adds a good amount of bass. Not too much and not too little, I figured I would give my review in case anyone else was looking at possible options.