Well, it needs to have HDMI with HDCP compatibility, ideally. Apart from that, it's up to you. The higher the brightness and contrast the better, response time is unimportant, all monitors have good enough response time for games.
hmm how can I find out if it supports HDCP, im planning on getting this http://ca.asus.com/Product.aspx?P_ID=LswHsbV9DN9vjQxS&content=specifications