Yes F11 does what you want with OS 10.4 and newer.

Wikipedia has a nice write up of this feature, called Expose. It can do more than just show the desktop and is a very handy feature to know how to use.

On older Macs I believe you can option click on the background and it will hide all windows and/or there is a finder menu command to hide application windows.
Source(s):
http://en.wikipedia.org/wiki/Expos%C3%A9_%28Mac_OS_X%29

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From the help screen on a Mac: (the Expose key will vary, it is F3 on my Macbook)

To hide all windows so you can see the desktop, press the Command (⌘) and Exposé keys together.
If your keyboard doesn’t have an Exposé key, press Fn-F11. (If your keyboard doesn’t have an Fn key, press F11.)
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Ok, people are not being clear with you. Expose only works if its enabled. To do so, go to the apple logo at the top left corner, and click system preferences. Click on Expose & Spaces in system preferences. Expose is this: http://upload.wikimedia.org/wikipedia/en/e/ea/Exposeleopardall.png
It lets you see all open programs.
And this is spaces:
http://en.wikipedia.org/wiki/File:Spaces.png
It gives you 4 or more desktops. (Each with the same icons, wallpaper).

You must enable these, and give them a key. On a apple keyboard from 2006 and later it will be the FN key with all the squares. Set Expose All Windows to that F key. Spaces is set in a similar manner, to whichever key you want.
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