"I want to connect 2 external monitors to my laptop, but it only has one video port. Is there some kind of add-on I can get to connect a second monitor"
There's plenty of evidence to indicate that using two screens are more effective than one; at least up to a certain point. There's also a strong indication that those two monitors need to be the same size, since your visual receptors appear to get confused by screens of different sizes.
A recent Utah study indicates that using 2 20-inch monitors allowed people to complete tasks 44% faster than using 1 18-inch monitor, making a pair of 20-inch screens from Dell for under $600 sound like a steal. Since many people I know have switched to using a laptop as their primary machine no matter where they are, the trick of using two monitors (at least when docked) can be crucial.
The trick I use for connecting 2 external monitors to my own laptop is to connect one to the external video port on my laptop and a second monitor gets connected to a DisplayLink adapter. The adapter connects via USB allowing you to extend your desktop to another screen. They are sold under a variety of brand names which makes the adapters a little tricky to track down, but a quick search of eBay for USB to DVI Adapter turns up several options that are basically the same thing under several different names. DisplayLink also links to several online stores, although they do a lousy job of labeling which country each store serves.