Maybe you all already know about it, but it was a pleasant surprise for me... I was shopping for a new sleeping mat and having a difficult time finding weight stats in one place when I stumbled upon Ultralight Outdoor Gear. I'm not sure that it will ever be the right place to buy (since it's in the UK), but it's a wonderful stat comparison site as they list the products from lightest to heaviest. Here is their sleeping mats page:
UOG - Sleeping mats
i really don't think that applies to me.