Source hydration packs are very good, better opening on the bladder than Camelbak's, they have a full width zip top to them which makes then very easy to fill & clean
I have the Source Spinner 2 pro it has enough room for tube, multi tool, tyre levers, cereal bars, pump, a few small spare parts (powerlink, tube patches & glue...) also can cram my soft shell into it too.
For most of my rides I use a Camelbak Blowfish, it's pretty big and can carry a helmet in it if needs be, as well as 3 litres of fluid and all the above stuff in the Spinner Pro plus a shock pump, another tube, chain links & still have more room in it spare!