sound deadening material?

i have a 92 Rodeo XS. when i am listening to music, the sound is less than desirable.   it sounds hollow inside and      outside, there is a lot of rattling going on, especially around the rear hatch. i know i am in dire need of some kind of sound dampening material but im not sure exactly how much or where to put it. i know ill need it on the roof (more so in the rear) and on the doors once i decide on a set of components (factory speakers are on the dash angled more toward the floor so im planning on installing a good ccomponent set in the doors). i also will need some on the firewall and maybe the floor to reduce excess engine and road noise. any suggestions on how much ill need and what areas to concentrate on? also any other brands besides Dynamat?   thanks in advance for any help.