http://store.apple.com/us_edu_112296/product/MB571Z/A?fnode=MTY1NDA5OQ#overview

$70 or best offer! Here's a bit about it:

Every Mac with a Mini DisplayPort allows you to connect an external display or projector using an adapter. You can use an external display as your main workspace or to extend your desktop, or you can work in mirrored mode with a projector so you can view what your audience sees.
Use the Mini DisplayPort to Dual-Link DVI Adapter to connect your Mac to a 30-inch display that includes a DVI connector, such as the 30-inch Apple Cinema Display HD, and enjoy the ultimate widescreen canvas with a resolution of 2560 by 1600 pixels.
Compatible only with Mac computers with Mini DisplayPort and Mac OS X v10.5.6 or later.