Dan,
I'd go with the Lowepro:
http://www.lowepro.com/Product....AW.aspxI've used it extensively for day trips in the alps. It is great - waterproof, with additional rain cover, enough room for lenses and a camera (even a 1ds), it has a tripod strap on the front and can accomodate additional pouches on the belt if you wish. The lower lens compartment can be left open while carrying the bag, so you can access the lenses WITHOUT taking it off. The upper compartment leaves room for food or even overnight change of clothes. And the compartment separator can be removed (even partially) to allow you to carry an occasional big lens (I use it for a 400mm 5.6). In addition it has two lateral netted pouches for small lenses, food or drinks. great pack !! Highly recommended :-)
Cheers Peter