The latest version of Witch, the indispensable window-switching utility, contains a new feature that highlights minimized windows with a border color of your choosing. When you activate Witch, you'll then be able to easily see your minimized windows, as their icons will have a unique border color. (Disclaimer: I was one of at least one users who asked for this feature, as I would occasionally activate a minimized window, and wanted some way to easily see them at a glance.)
As shipped, the minimized windows are shown in the normal window hierarchy. What I wanted, though, was a way to sort of mirror the Dock's view of minimized windows -- I wanted to see all of my minimized windows grouped together. Thanks to a hidden Witch preference, you can do just that. First, disable Witch and close its System Preferences panel, then open Terminal and paste this command:
Mac OS X Hints
http://hints.macworld.com/article.php?story=20081125053213606