Elizabeth, and everyone,
The new Apple monitors come as large as 30 inches (less scrolling; see the whole width of your portrait at once)!!! But they are probably too expensive and precious to use at an easel, at least for most of us. It's okay to dream of having one, isn't it?
http://store.apple.com/1-800-MY-APPL....2.1.3.0.0.1.0
Another option to consider is the all-new iMac G5. This is a self contained 2 inch thick machine with a built in flatscreen 17 inch or 20 inch display:
http://www.apple.com/imac/
Garth