The Dell 2408WFP has a reputation for high input lag (50ms - 60ms). They have released 2 revisions since version A00 which decreased input lag gradually. The current and last version is A02, however there have been no test to check input lag of the current revision (at least not that I have found).
The Planar PX2611w not only uses a H-IPS panel for better color accuracy (when calibrated) and has been tested to have <8ms of input (or < 0.5 frames) by ToastyX, a respected member of www.Hardforum.com who has a lot of Display [LCD monitors] knowledge.
Bad for console games because of color banding issues when playing console games (Xbox 360, PS3) at 1080i/p resolution.