Televisions are switching to widescreen displays, 16:9 aspect ratios like a movie screen instead of the more square 4:3 aspect ratio. Computer monitors are following the same path; I’m now recommending 20″ widescreen monitors for anyone buying a new computer. (You may not be able to run the widescreen display correctly on your current computer – the video card has to support a widescreen ratio, typically 1680×1050, or things will be stretched incorrectly.)
Dell’s Ultrasharp monitors have been reliable choices for years – high quality displays for a reasonable price. If you’re buying a new computer, consider the Dell Ultrasharp 2007FWP, typically $400, occasionally a bit less. Here’s an article reviewing the Dell 20″ widescreen and a couple of competitors.