DVI really makes a difference. Get one that supports it, so if you upgrade your graphics card later, you will have it. Be sure to get over 500:1 contrast ratio. 700:1 or higher is better. Also, make sure its under 12ms, as those have said.
Do you play games? If you do, get the 17" one if you don't want to upgrade your graphics card. The 17" LCDs look much better at the gaming resolution of 1024x768 than the 19" monitors do. However, this wont be an issue if you get a good graphics card.