SoundGraph has introduced some devices called FingerVU that function as USB sub-monitors. They come in 4.3″ and 7″ screen sizes. You won’t need a mouse and keyboard to manipulate what’s on them since the FingerVU works independently of the main monitor using touch and SoundGraph’s own FingerUI interface.
These are probably good for watching videos or RSS feeds while you work on other stuff on the main screen. Twitter addicts will want to use it for their Twitter feed.