For which computer?
I have 2 main computers - a Windows 2008 server and a HTPC. Both plug into my 42" LCD HDTV at 1900x1080. The server will have a 19" CRT for a second display and the HTPC (which is also my general use computer) will have a 22" LCD in portrait mode (I do more web browsing and document writing than anything else on that one).
My 3rd personal computer will be set up using my 2 17" CRTs I have sitting around.
My wife only need a 19" LCD (and she says that's even more than she wanted), but it was really cheap.
For my mother, I set up her mac mini to display on a 19" LCD through a EVGA USB graphics adapter. Her main display is TV Out to an old 27" TV (so she can fall asleep watching Hulu movies).
Yup, that covers my family's set up...