Look for a 1920x1080/1200 resolution, 5ms or less response time, LED backlighting and preferably VESA mounting. If you had a bit more money, a 120hz monitor is also a good idea. As that will allow an FPS of up 120 to be displayed, and can also show a 3D image.
TL;DR: This monitor is fairly good for your budget.
Asus VE248H Black 24". $200 ($15 rebate)http://www.newegg.com/Product/Product.aspx?Item=N82E16824236102