Look for a response time UNDER 16ms.
If you look at the better ones, there's a "gaming LCD" down to 2ms, but I bet it cost $900.00. Look for 16ms or better. I'd suggest something with a max resolution of 1280x1024 (but that's my personal taste), and any other features you might like.
My LCD now (a Dell 1900FP) is nice, it has USB ports and looks great, but the response time is 26ms, and the pixels "blur" and streak when moving. You get used to it, but it's a detraction when playing AH.