To add to this thread, I just used a Pacsafe bag on a week long trip in Asia. It was extremely comfortable and light. I will probably add a crumpler sleeve inside to hold my SLR next time, but it was fine with some extra padding to carry around an SLR and an extra lens. There are two water bottle pockets on the side, and alternatively you can add a hydration pack as well. I brought the pouch from my camelback and it worked out well on a light hike.
http://pacsafe.com/www/index.php?_ro...=detail&id=231