I have 1 speaker in each door (like above but without the custom door panels), 6x9's in homemade boxes above the rear wheel wells, 10" sub box mounted under the rear seat (Sony XPlod setup) with an amp for the sub mounted under the passenger seat. All of it's run by a Sony head unit in a Tuffy console. It sounds pretty good, gets pleanty loud, and the sub adds just enough bottom to help without thumping.
As soon as it comes in, though, I'm going to move the door speakers up to the BC Broncos wiper motor cover so that I can actually hear them. Being down low on my doors makes them really hard to hear.