The Sony W900A, is one of the leading tv's for input lag at 18ms, especially in your price range. Unfortunately, it only comes in 55". Everything I have read about this tv (trust me, it has been a lot) has been really promising. From its quick input lag to its Triluminos display technology(which is unique to Sony). This tv really shines, even when compared to higher priced tvs. If your looking for a gaming tv or just a tv in general and you can deal with a 55", I'll go on record and say this tv is the best one you can get for under 2k.
Might I add, if you want a Plasma, the Panosonic ST60 is pretty freaking sweet as well. A buddy of mine has this tv and it is very, very impressive, unfortunately, the input lag sucks compared to others. Comes in 50,55,60, and 65" I think so you have your options. I think the 60' is around 1.5k