I just picked up a new pack so I can ride with my 10D. After looking around for something along these lines, and thinking hard about modifing a "real waterproof camera pack". I got a second high recomendation for this "little" jem. for those intrested it's a Deuter TransAlp30. (~1800 cu. in. storage, 3L fluid bladder, integrated rain fly)
It easily hold all my bike gear, plus I can fit my tamerac bag with the 10D, 17-40mm, 550EX ( Ed. Note: I need to learn to control this thing!), and extra bateries/stuff.
I took it out tonight for the first time. BUt got dark too quick for me to take many shots. The pack rides quite nice, and will be put to good use this weekend with 4 rides planed in New Hampshire, western Mass. and southern Maine.