I've got an old Dell 21" (Ultrascan 21FS-BN) with a switchbox to my laptop and desktop.
Laptop is running at 1024x768
Desktop is running at 1280x1024
Monitor goes up to 1600x1200, but only at 60Hz.
21" is a great investment though, only problem is when you've had one for years, and want a new monitor with a better res/refresh rate, it'll cost a fortune, because you won't be willing to go to anything lower than 21".