What kind of monitor do you want? 60hz/120hz\144hz?
For great colour clarity it games, It will be either IPS or PLS panel which are 60hz. If you want the fastest response times and high refresh rates, a 120hz/144hz monitor would be best. The downside to higher refresh rate monitors is the lower colour depth and accuracy.
Here are 2 options within your budget you could choose:
BenQ XL2420TE 144Hz
Youtube review by Linus, himself:
http://www.youtube.com/watch?v=I6wIMaYjklE
ASUS VX279Q 27-Inch Screen
Unfortunately, Linus hasn't done a review of the Asus monitor.