Today you can find 18.4 inch displays. Start with the Toshiba i3 powered P500 line.
A few years back, HP came out with a 20-something inch "laptop" ... and then IIRC Dell struck back with their own 24 inch "portable" computer. I immediately began to lust after those (and similar from other manufacturers) devices, but at the time they were way hecka out of my price range.
Now I can afford one (based on their price of 3 or 5 years ago) but they don't seem to exist any longer as far as I can see.
Does anybody know of any current large-screen (greater than 20 inches diagonal) "laptop" computers?