There's a new device on Kickstarter called "Sliden'Joy" that adds one or two HD displays to your laptop. They're light, thin and will offer 3 sizes: 13", 15", 17" so that you can take them with you when you travel to have the multidisplay experience.
The prototype is less than 2 cm / 0.8" thick - the production version may be a little thinner. It attaches magnetically to the back of your display and the extra displays slide out from either side.
It will work with either a Mac or PC connecting to the laptop via USB (and powered by USB as well.) The displays can be angled in different directions for desktop presentations.
It looks like a 2 display version will start around $350 and a single display version, around $250. With about a month to go in the Kickstarter, no production/delivery date has been set.
For more info: