If you are amenable...
Gaming:
--- 1920x1200 has 19% more pixels than 1600x1200. We are not talking about orders of magnitudes.
--- The need for AA and AF is much lower (if any) at higher resolutions.
--- In the worst of cases, setting the resolution at 1280x800 will still give beautiful results while being much easier on the videocard.
--- Most newer games are designed with widescreen compatibility modes.
Video:
--- All movies and TV programs are now shot in widescreen.
--- Widescreen camcorders are spreading fast.
--- 1920x1200 can display 1920x1200 HD video without scaling. 1600x1200 can't.
--- Newer wide 24-inchers such as the Dell have HDCP. Will be able to work with affordable HD burners in a couple of years.
--- Would you buy a 4:3 TV set today?
Work:
--- Easier to work with windows open side-by-side than on top of each other.
Market:
With 20 and 21 inch 4:3 screens being older products, it's hard to find a very good price. The strongest competition today is in entry-level 19-inch 5:4 monitors and 19-inch to 22-inch widescreens. 24-inchers are next. The Inquirer predicts (and I agree, for what it's worth) that the $500 24-inch 1920x1200 widescreen is for this year. It will be exciting in the coming months with a flurry of releases from Samsung, LG and Viewsonic among others. Besides this, it seems the 4:3 monitors are all old inventory at old prices. Nothing seems to be on the horizon.