Hydration paks.

I use the UltrAspire Surge. I *LOVE* it. Doesn't not jostle, weight sits higher on the back and there is NO strain on my shoulders. I had 3 or 4 friends buy it as well after I recommended it and they love it too. I really think the 2 chest straps, lines of the front pouches and side adjustments make it fit so well.

It has 2 pouches in the front, with another front compartment (so, 2 plus a small 3rd), a top zipper pouch and then the compartment for the water, then another outside compartment that's not fully closed. I shove things down there, like this weekend a Vapur water bottle & baby wipes and it never fell out.

Unfortunately, like shoes, everyone has to try different ones, but I won't be trying another brand for a long time. If I need a bigger pack, I'll buy another one of theirs. That said, I've worn this for 50m without comfort issue. I haven't done training runs where I need a bigger pack yet, but it's always carried more than enough water for me between aid stations. I know I could easily do several hours without refilling it.

http://www.ultraspirestore.com/Surge-Select-Color-SP13-p/ua053xx.htm

Mine has a sliding top, the bladder top folds over itself, and a bar slides over the fold to keep it sealed. I like it better than the twist circle close bladders.

Based largely on the feedback here I went with the Nathan and used it for the first time last night.  Works pretty well.  The long strap ends were bugging me as they danced around.  Had to reach down and stuff the ends under the straps.  Didn't think this was a great long term solution because of potential chaffing.  Do you cut them shorter?

Also, even after rinsing the bladder before using it had a horrible plastic/rubber taste.  I assume this will eventually go away.  How hard are these things to clean if you are using some kind of sport drink?  I guess just rinse after each use?