From our experience with such previous postings as the multiple mutant monitors, we know now that there's no such thing as two many screens for many Cravers out there. And if they're built into a dual touch-screen laptop, all the better.
But what if you want a more conventional keyboard set-up while saving footprint space on your desk? An outfit called Neuro Logic Systems, which has made products primarily for the medical field, has developed what it calls "the the world's first dual 19-inch LCD in a vertical format." It's not exactly portable, as OhGizmo points out, but the configuration does show what dual vertical screens would look like on a laptop, folding up when they're not in use. If you're just looking for dual desktop monitors, you might be better off with a pair of horizontal Siamese monitors.