I'm a web designer so it's nice to have everything up at once. I put my email, aim, etc. on my right monitor, all my folders, shortcuts, etc. on the left one for quick access, my graphics editor on my left 30" and and code on the right 30". I'll also usually have up Firefox, Opera, IE 6 and 7, and Safari to check for browser compatibility, so when I use Ultramon I can keep all browsers up on either the right or left monitor in a separate taskbar ready to view without having to take down fireworks/photoshop or dreamweaver, or shrink their window sizes.
Though these monitors did cost me a bit, and not everyone has money to spend on something as excessive, I honestly think investing in a good 24" monitor would be a wise choice. You're going to get a great quality image, and the resolution jump from 22" to 24" is quite significant. Honestly, you could probably even find a mid range 24" monitor out right now for less than 400, I just recommended the 2408wfp because it's probably one of the best 24" displays imo.