If you have multiple stacks in the dock, it is helpful to be able to quickly identify them. Unfortunately, in 10.5 the way in which Stacks work causes, for example, Address Book (or whatever your first app in Applications is) to be used as the icon for the Applications folder in the dock. This makes it hard to identify your docked folders at a glance.

To work around this, open Automator and create a new fake Automator project -- it can be completely empty, in fact (choose Custom from the selector when Automator launches). When the project window appears, choose File -> Save, set the Format to Application, give it a name that comes very early in the alphabet -- AAA or similar. For the save location, point to your Applications folder and save it there.

Back in the Finder, Get Info (Command-I) on both the Applications folder and your new AAA "application." Copy the icon from the Applications folder (by clicking on the icon in the Get Info window and pressing Command-C), then paste it onto the icon in the AAA Get Info window. Finally, drag the Applications folder into the dock. (You may need to remove and re-add it if it was already there). Make sure that it is set to display sorted by name.

[robg adds: This is the best solution I've seen to this problem, though I think it can be simplified: you don't need Automator. Just create a new folder, name it AAAA (I use underscores, to make sure it will always come first: ___A), and then paste on the custom icon. It seemed to work just as well as the Automator solution. The only downside to this method is that you'll see your custom folder/app as the first item in your stack, but that's a small price to pay for icon consistency in the Dock.

The other solution I've seen mentioned is to put an alias to the folder in the folder, but this leaves you with the alias arrow (and can be quite confusing in the Finder if you click the alias). Note that this is different than this hint, which explains how to basically disable the Stacks functionality of docked folders.]