I learned a pretty useful trick for my Mac Book Pro. I use it for presentations, and I’ve been restarting it whenever I plug it into a projector. With this tip, I don’t have to.
1. Press the Apple key > Sleep.
2. Plug in and turn on the display.
3. Press the Escape key to wake the computer.
And that’s it. Open System Preferences > Displays to turn Mirroring on or off as needed.
Source: Mac OS X Leopard Pocket Guide