monitor upgrade

First off you need to know what you want from your monitor. Do you want to watch HD content on it ? What type of connections do you need/want.
I could start throwing numbers at you for Contrast and Response times. I could start talking about dot pitch and various other technical specs.
I wont though what i will say is find out the answer to the what do you want from it question and then go and physically look at some monitors and find one you like. There is no substitute for getting to grips first hand with a monitor. A good shop will help you and let you adjust and tweak settings on the monitors. Show you how it looks with a PC image and a HD image. This is important as you will presumably be spending quite a while looking at it. Just ordering one online that meets a set of specs is fine if you just want a cheap one, however if you want a decent one go look at it even if you order it online later you will know exactly what you are getting.

Mactronix

Honestly, budget is the only thing that will stop you. I simply recommend to wait for rebates.

Other users have mentioned response time, this is something I usually don't spend a lot of time on, I won't settle for anything over 5ms, but I don't believe 2ms is worth the extra money.

What you should worry the most about at the moment is the resolution, most 19" have their resolution up in the 1200 range or in the 1400 if you're lucky.

Here's what I have, and let me tell you that it has been the best purchase in my life:

LG 22" 1680x1050 5ms 3000:1 Contrast Ratio.

I got this screen about a year ago for 279.99 (took the demo with a huge rebate). These LCDs cost around 375 back then.

You can get similar LCDs today for around $200, you can't go wrong. Just keep in mind that cost just keeps dropping, for the same price range, I can now get a 24" 2ms 1920x1080 7000:1 Contrast Ratio (about $375).

If you have $200 to spend, 1680x1050 resolution on a 22" display is the best way to go in my opinion.