DragThing

Here's a screenshot of my DragThing configuration. It's a collapsible drawer against the right hand side of the screen, with 11 clickable tabs that activate separate layers. The icon drawn in each layer's tab represents the category of apps I place there: Home, Palm, Internet, Productivity, Browsers, Communications, Utilities, Games, Moviemaking, QuckTime, and Graphics.

Clicking the active tab hides the dock, leaving only the tabs. When inactive it also becomes semitransparent.

Each individual item is clickable to launch an app, but can also be used to reveal the target item's location, quit the application, or edit the button itself.