Sub and Amp combo from crutchfield, its the tube type so it dosen't take up much space, and from what I heard it provides decent bass, just don't expect to feel it half a mile away.
Bazooka Bass Package CST8012 8'' bass tubeCSA150.1 mono amplifier at Crutchfield.com
not sure about the back speakers, crutchfield can show you which ones fit, its a great site.