⌥+⌘+M as mentioned in multiple docs only appears to minimize the current (focused) window.
I am looking for the "Show Desktop" equivalent. If it matters I'm using 10.6.4.
⌥+⌘+M actually minimizes all windows of a current application, not just the current focused window (unless of course, the application you have running only has one non-minimized window.)
The easiest way to hide all active applications is to select the Finder/Desktop, and then "Hide Others." The keyboard shortcut is ⌥+⌘+H.
You can also simply hold ⌥ and ⌘ and click on the Desktop, or Finder on the Dock, or of course, simply use Expose and hit F11 (Or whatever you've rebound Hide-all to.)
I just use Hot Corners to do it.
System Preferences >> Desktop & Screen Saver >> Hot Corners >> Select "Desktop" from one of the dropdowns. I use the bottom left, since that's where I was used to the Desktop button in XP lol.