Toggle Display Mode On Newer Mac Laptop Keyboards

From MacOSXhints.com

The new keyboard found on MacBooks and MacBook Pros now contain Dashboard, Exposé, and media controls on the function keys, but removed the toggle between mirror mode and extended desktop mode. On the prior keyboards, the toggle display mode function was located on the F7 key.

On the new keyboards, you toggle display modes by pressing Command-F1. This only seems to work from the built-in laptop keyboard.