I can't tell you a specific one, some major deciding factors should be the reponce time and resolution of the LCD. Realize the screen gets blurry at lower resolutions, so if you want the clear pic, you MUST play games at the native resolution. Responce time, usally you want something less than 12ms, I hear people saying less than 6ms. I'm fine with mine at something around 6-8ms, but of course the faster the less ghosting you'll get.
Another thing to consider is if you want wide screen or not. Personally, I hate wide screen. I'm sure in a bit basically all games will support it, but currently, not too many do.