Apple Mini-DVI to DVI Adapter
The Mini-DVI to DVI adapter is designed for the iMac (Intel Core Duo), MacBook, and 12-inch PowerBook G4 -- allowing you to connect to an external DVI monitor. It can also be used in combination with the Apple DVI to ADC adapter to support older Apple flat panel Studio or Cinema Displays.
Price: $19.00
OR, if you have a CRT or LCD without DVI, get the Mini-DVI to VGA version for the same price.
MacBook supports spanning out of the box, so you'll be able to enjoy dual-monitor goodness!