OCModShop posted a review on the DisplayLink USB Graphics Adapter
Regardless of your reasons, people are now used to running multiple monitors in everyday situations... but not every computer is equipped with multiple display ports. Some monster cards, like the Sapphire 4850 X2 reviewed here, have four DVI ports, which is more than enough for even Al Gore. Most add-on graphics cards only have 2 ports, and only one of them may be DVI. Notebooks (and netbooks) usually only have a single VGA port, if they have one at all. If only there was some way to upgrade your monitor and desktop space without opening your computer...DisplayLink USB Graphics Adapter Review
DisplayLink has the answer with their innovative USB to Graphics adaptors. These little devices are small little boxes that plug into a USB port, and then connect to any DVI or VGA monitor. The software uses your existing video card's capabilities, so even full-motion video and 3D accelleration is still possible on your other monitors.