I did the floor of my cab this summer using a heat/sound insulation kit from JC Whitney.
It's similar to carpet padding with a metal backing on it. This makes it much thicker than I was expecting but I think it worked well and for $50 you get more than enough to cover your whole cab floor. As for sound deadening results its hard to gauge considering I only did the floor but road noise in my truck doesn't bother me and I've drive it on the highway to work everyday so it must have done something