There's the slightly smaller Dell U2312HM which also uses an e-IPS panel. It has been tested to have a 0.6ms input lag time (not to be confused with response time). That mean the time it take for your actions (like in a game) to be reflected on the screen is extremely small even when compared to TN panel monitors.
Otherwise the Dell U2412M is a good choice as well
U2312HM review:
http://www.tftcentral.co.uk/reviews/dell_u2312hm.htm
U2412M review:
http://www.tftcentral.co.uk/reviews/dell_u2412m.htm