I have the Velbon super mag slider focus rail, it is fairly quick and easy to use and is adjustable backwards, forwards and sideways, I have only really used it backwards and forward for focus stacking it is quick and easy to mount the camera on. The adjustment screws are quick and easy to adjust!
I have used it with a Canon 7D and EF100mm F2.8L IS Macro lens and it seemed to manage the weight okay,
I looked at various options and this seem to be the one that came out best for my budget.
This shot was taken with it:-
