figured i'd chime in. i picked up a 1996 tacoma as a secondary vehicle so didn't want to spend a lot of money going all out on deadening.
i found some very reasonably priced "Dynomat" on ebay
and followed that with a layer of yoga mat. you can pick up a yoga mat for ~$5 at any discount store. Took me 50 sq feet of "Dynomat" and 3 yoga mats to cover everything except the headliner in my extended cab. A yoga mat is a closed cell foam...and reasonably priced.
my primary car is a Lexus IS350. Does the Tacoma now sound like it? no. but it sounds better than it did before. road noise is still the same, but it is night and day more solid over bumps, and the stereo sounds better. the doors now close with a solid thud, with no tinny/flimsy feel to them.
I would do this again in a heartbeat for the $100 it cost me. Seeing its not my primary vehicle and just a toy, i wanted the best bang for the buck...and i feel like i got it.
From what I've read, MLV is the way to go. One site I read compared the effects of MLV to lead. Imagine what a layer of lead all around your truck would do...and MLV does that at a fraction of the cost.