Charles O’Rourke : Hierarchy:
With the release of Mac OS X 10.5.0, Apple took away a feature of the Dock that had been present since Mac OS X 10.0 — the ability to right-click (or control-click) on a folder in the Dock and see a hierarchical menu of the contents of the Dock.
Hopefully Apple will restore this functionality to the Dock in a 10.5.x update, but in the meantime, Hierarchy is a freeware application that will create a small palette that replaces the functionality of placing folders in the Dock. Any folders or files can be dropped into the Hierarchy palette. Files can be launched from the palette, and folders can either be opened in the Finder with a left click or browsed in a hierarchical menu by right- (or control-) clicking.