Minimize and Hide All Windows in Mac OS X with Command+Option+H+M
By combining the Hide All shortcut with the minimize keyboard shortcut in Mac OS X Lion, you can use a third ‘Minimize and Hide All’ shortcut by hitting the Command+Option+H+M keys.
As the title suggests, this keyboard shortcut will hide all other applications and windows, in addition to minimizing the currently active application or window, effectively clearing the entire screen and giving you a blank view of the desktop. If you have Dock icon translucency enabled as shown in the screenshot, the hidden apps will appear as translucent while the minimized windows from the foremost app will be in the Dock separately.
Heads up to @sambrowne for the tip.