Following on from my KVM post here is another little trick. Sometimes I just want a bigger screen for my macbook, I don't want two screens especially when I am working with a large number of paper documents simultaneously. MacBooks have a great feature called clamshell that allows you to just use the external monitor.
1. Set your MacBook up with a USB keyboard and mouse
2. Plug in an external monitor.
3. Close the lid and jiggle the mouse.
If you are lucky you will see your desktop and you will be back to a single monitor, occasionally your mac will decide to sleep but if you are insistent it will wake up again.