A bunch of you were checking out my hydration backpack this weekend so I thought I would post up some info about it. They cater to the biking industry so you'll have to go to a bike shop to find one or online, ebay is the best place to start because they are around 130 retail. But IMO worth every penny keeping my back cool. What everyone at the rally loved about my pack is how it kept your back cool. It has a "bow" design so it keeps the pack away from your back and just a layer of mesh against you. And with the pack away from your back it pulls in air from the side and keeps you cool. Another nice thing that people notice is how the entire top of the reservoir opens up to add ice or for easy cleaning. I've has quite a few of the hydration backpacks out there such as camelbak but this is by far the best one I've found.
http://www.deuterusa.com/products/productDetail.php?packID=RaceEXPAir&sub=hydration&tert=race
http://cgi.ebay.com/NWT-Deuter-Race-EXP-Air-Pack-Black-Silver_W0QQitemZ320385706320QQcmdZViewItemQQptZCycling_Parts_Accessories?hash=item4a9879e950&_trksid=p3286.c0.m14&_trkparms=65%3A12|66%3A2|39%3A1|72%3A1205|240%3A1318|301%3A1|293%3A1|294%3A50
http://cgi.ebay.com/Deuter-Race-EXP-Air-Hydration-Pack-MTB_W0QQitemZ250449431857QQcmdZViewItemQQptZCycling_Parts_Accessories?hash=item3a4ff30d31&_trksid=p3286.c0.m14&_trkparms=65%3A12|66%3A2|39%3A1|72%3A1205|240%3A1318|301%3A1|293%3A1|294%3A50