a million and one threads on this but dynamat is your best choice. Probably ebay is the best place to buy it since its going to be the cheapest around and there are no worries on warranty.
My car audio:
CD tuner: Alpine CDA-9884E with Ipod interface
Front speakers: Alpine Type R SPR-17S 6.5 component speakers, powered by a avant-garde 23dxi 2 channel amplifier - 2x51 watt RMS
Rear speakers: pioneer coaxials connected to tuner
Subwoofer: Alpine Type R SWR-1222D 12" 2 ohm dual voice coil 500 watts RMS powered by a response precision 2x150 watts RMS 2 channel amp bridged to 500 watts RMS @ 4 ohms