Are there external video cards for laptops?

I have a laptop with a nvidia gforce8400 and i want to get an upgrade, however I understand that you cant upgrade laptop video cards because they are set to the mother board. I heard about external graphic cards that you plug in through usb or something. Anyone know of these? im trying to get video card for games and stuff.|||yes there are but they are not available to consumers yet.|||the USB ones are true but they will only allow you to get more monitors, they will not increase performance as far as i know.