If you are like me, there is just not enough room in the dock to put all your favorite stuff. I used to use a program called Drag Thing (a $29 Shareware application) in Tiger. However, when STACKS were introduced in Leopard, I realized that I could replace the functionality of Drag Thing (that I used) with a creative use of stacks. For the record, Drag Thing remains a great application for organizing all your favorite stuff and keeping it just a click away, but it was more than I needed.
So here is the scoop on how I organize my dock with stacks.
1. Choose a place to hold some organizing folders (your documents folder maybe) and create a folder for each "bucket" of applications you want to group together. The ones I made were ...
Favorites . Office . Geek Stuff . iStuff . Graphics + Media . Fun
(note: the label you choose will show up when you hover over that dock item)
2. Make aliases for you applications and drag those aliases into your folders
(tip: if you hold "command" + "option" key while you drag the icon to the folder, you can auto create an alias w/out the word "alias" appended to the name... always check that the icon you created has the arrow that indicates it is an icon. If it does not, then you moved the file and should move it back and try again.)
3. Drag each folder to your dock (to the right of the separator bar)
4. Click and hold on the folder icon until you get a popup menu. Make sure it is set to stack (instead of folder) and set to automatic. This will make folders with fewer items display as a fan and more populated folders (like my geek stuff folder) display in a grid)
Your done. Now you have quick organized access to some of your favorite applications.
(note: the application that is the FIRST alphabetically will be the top icon for the stack.... to pick the one you want, just type a * (shifted 8) in front of the name and it will move to the top and be the icon for that stack)
One last note... you can use this same technique to get quick access to folders full of files (rather than applications aliases) by simply dragging the folder to the dock and setting it to "folder" vs "stack". The downloads folder in your dock is an example of this, but you can put any folder you like in the dock as well. Lots of our clients have the folder to their most current project files in the dock for quick access.