The Amphipod RunLite hydration belt is an excellent tool to maintaining hydration on long runs. It consists of several smaller bottles that are attached to the belt and come unclipped for on-the-go hydration.
Because there are several smaller bottles, it is possible to distribute the weight of the fluid carried during a run. It is also nice because fluid other than water (e.g., Gatorade) can be placed in some of the bottles while the others contain water.
This is not an innovation unique to Amphipod, but they have excecuted the idea well. The belt is wide enough so that it doesn't cut into you while running, and is relatively comfortable. The 8 oz. bottles are generous in size and clip in and are easily removed while running. The top is easy to open on the run, and the mouth of the bottle is large enough to clean well (a complaint I've had with FuelBelt's model).
This company offers several models, each having a different bottle number and configuration. So, the hydration needs of many different running types will be satisfied with this system.
These belts can be found in many local running stores, and locations of the running stores are given on their website.