IPS monitors are going to be the best bet for gaming because you get near-perfect brightness across the screen no matter where your viewing point is. And if possible, Matte>Gloss for IPS panels. All the above suggestions are fantastic. ASUS monitors are currently outperforming the previous DELL mega-monitor series because of their bargain prices for what they are delivering.
Forgot to mention. Get a tn panel for gaming only purpose. Get an ips monitor if doing anything else like watching movies, etc.
Is there a down side to using the IPS panel for gaming?
Generally, TN panels have a faster refresh rate and therefore will be a little smoother in some sections with fast motion compared to an IPS panel. But IPS panels usually have better color accuracy and brightness across their display.
IPS screens usually run around 60hz like most screens, so you're really not going to notice much of a difference whatsoever.