I tend to hook up my MacBook on one of my external displays when I sit at my desk. I have two 22″ screens, one which I use for the MacBook the other I used for my desktop PC. A while ago I gave that one away and so the other screen was only gathering dust.
The MacBook only has one external display port so in order to hook up two displays you need to do some research. One possible solution is the DualHead2Go from Matrox. You hook this up on your display port and it basically directs half of the signal to one screen and half to the other. So you need to set your resolution to a rather big one, the MacBook is not powerfull to power two displays at 1680 * 1050. It wil also set you back around 300$/€.
Then there’s ViDock, a very powerfull solution but it comes with a powerful price, almost a new laptop (700$/€).
And then there’s DisplayLink‘s technology, which enables displays to connect via USB. They’ve been around for some time and now have drivers supports Mac OS X. I went for this solution from EVGA, compared to the others it’s relativly cheap at around 70$/€ for their best model (UV-16 +). Which can power displays up to 1680 * 1050, just the resolution I wanted. While it can’t play HD content smoothly, normal usage is just fine.