Kensington is offering its Mac and PC-compatible Dual Monitor Adapter. It costs $119.99.
The Dual Monitor Adapter, powered by DisplayLink technology, enables you to connect a second display to your computer using the USB 2.0 interface instead of an external video port. The adapter connects to a DVI-compatible monitor; it can work with an older analog display using a DVI-to-VGA adapter.
DisplayLink began offering preliminary support for the Macintosh earlier this year using beta software drivers. The company hasn’t been able to make much headway with its Mac drivers; in an interview with Macworld in April, the company’s director of marketing said that Apple needs to document its graphics hardware better in order for DisplayLink products to work optimally on the Mac.
System requirements call for Mac OS X v10.4.11 or later.