I was giving a presentation on my Acer Aspire One netbook recently, and it occured to me that there must be a better way to enable the external display than to restart X. With my old laptop I had the nVidia control panel to control external devices, but this netbook has an integrated Intel GMA display adaptor. It turns out that xrandr (and the GUI front ends) fit the bill nicely.

Basic stuff:
xrandr -q
This displays the information of the currently connected displays.

xrandr --output LVDS --off --output VGA --mode 1024x768
This turns off the internal display and enables the VGA connected device at a resolution of 1024x768. The option you pass to mode should be listed when you run -q.