Another vote for an Osprey. On rides <~80 miles I'll tend to just take bottles, but on long sunny rides I like a hydration pack.
I also use it for my commute, as the small/thin size means it makes my back less sweaty than a normal rucksack - the Viper 9 easily fits a change of clothes, lunch, and camera when I leave the bladder at home.
I also use it for my commute, as the small/thin size means it makes my back less sweaty than a normal rucksack - the Viper 9 easily fits a change of clothes, lunch, and camera when I leave the bladder at home.