RAAMaudio - Quality and Value in Automotive Sound Deadening
Cheaper and better than Dynamat (Yes, I've used both) Get Some RaamMat and Ensolite foam, a few cans of his spray adhesive and you are good to go.
He has also got a good "How To" section, read through that. Its really not that hard to do, if you are comfortable popping off panels and pulling up carpet (Should be pretty easy on most vehicles)
Good luck!
- Andrew