Dolly sliders are all the rage right now. Finding the right dolly for the right camera can be a challenge. One day you are shooting with the 5D, the next it's a full on package with long zoom and all the accessories. We found a slider that works for just about any camera. It's called the Blue Plate Special.
It rides on standard 1.25" speed rail. We use 4' pipes but it can be expanded to any size up to 20'. Probably the wrong tool if you need a 20' move, but it is possible. Can mount directly to head with Mitchell mount or 100mm ball adapter.