DynaXorb:It's like a big slab of soft licorice! Wierd gel type material but absorbs resonant frequencies.
NOTE: You'll need a tube of superglue to install it!! Nothing else works, trust me!!!!
EDIT: I've just found this: Dynamat 11855 Dynaxorb Sub pack
It's a Dynaxorb 8 pack. So you get 8 Dynaxorb pads (same size as single pair packs) but it's $125 which works out ~$20 cheaper than buying the boxes individually. Also has glue with it.
NOW, How much do people need:
Dynaxorb comes as a set of 2 pads (one pad per door). Typically only installed in front doors, but you could put them in the rears if you REAAAALY want. Honestly, you won't hear the difference in the rears.
Dynamat Extreme Bulk PackI've used one of these and have done:
Front doors (outer metal skin)
Front doors (Inner metal skin (that the speakers are bolted to))
Rear doors (outer metal skin)
Rear doors (a 30cm square around the speaker mount)
Rear parcel shelf (the entire metal shelf - it's a sedan)
Some areas around the rear wheel arches (with scraps)
and I still have 1 full sheet left.
If you have a Sedan, a full box will let you do all doors inside and out and the parcel shelf *just*
If you have a Wagon, a full box will let you do all doors inside and out and some of the tailgate.
If you only do an outer (or inner) layer on the rear doors, you're left with more spare to do other trouble spots, like wheel arches and tailgates (wagoners).
IF you have a boxed sub in the boot, DONT do the parcel shelf. It'll stop the sub sound getting into the cabin! Deaden the boot lid, wheel arches and outer skin of the car behind the crappy thin boot liner.
Honestly, there'll be a few people come away from the day with spare sheets and they'll be traded on here so you'll be able to pick up some spares for small amounts if you need to top up areas (like boot installs).