Dampening material used in a hi-end car system?

I would like to have some input on dampening material used with your car system.
What kind you prefer?
How much to use?
Where to use it?

I have dampened my pick-up, and went way over kill with it. With three layers of dynomat on every sheet metal surface and one layer on the back of all the plastic. And it has made a huge difference in the sound quality of my stereo.
So please tell us your experience with your form of dampening, and the out come with it.

Dynamat is stupid expensive. I've found the foamy stuff you line cabinets/drawers with works well at a fraction of the cost. Just a little spray-on sticky glue and you're golden!

It is over priced, I have a friend that owns a local stereo shop and he hooked me up with a butt load at there cost. But still pretty pricy. I have seen sprayable stuff that would be more cost effective, it comes in a five gallon can and it should go a long ways. I've heard that the spray on bed liner stuff works good but it's high to.

The bedliner doesn't have near enough damping to control resonance.

A local line-X company has been making a fortune spraying trunks of cars at (500.00 a wack). I didn't think it was pliable enough for dampening, but they are making a ton of money for it.

Get RAAMat- it is hands-down the most economical and it is now made from butyl rubber and not tar (alum/sticky rubber). The service is great (Rick) and he often sells on eBay....