Originally Posted by frito
there are 3 factors that contribute to input lag
That is by far the most succinct and detailed description of the causes of input lag that I've seen anywhere.
I guess this means the short answer to the input lag question is: find a set with an IPS panel. IPS-Alpha is better than S-IPS, but both are much better than the various forms of VA panels that are used in most sets. The price you pay is poor black levels.
The specific sets I've seen mentioned so far are:
TC-L32S1, L37S1, L32X1
These all use IPS-Alpha panels, and have the lowest lag available.
Not IPS-Alpha (probably S-IPS), but still low lag
TC-L42U12 (Best Buy Exclusive)
Some of these use S-IPS panels, and some VA. The IPS sets have low lag, the VA sets don't. You can look closely at the pixel structure to see which panel a particular set has.
37LH20 - I bought one in January, which has an S-IPS panel. Decently low lag, maybe not quite as good as the Panasonics.
37LH30 - early production units are S-IPS with low lag, current units are VA with high lag.
Various other LH-series sets - Unknown, and probably vary between production runs.
I don't know of any other specific brands/models that have IPS panels. "IPS Alpha Technology Limited" is a joint venture of Hitachi, Toshiba and Matsushita (Panasonic), so they will probably show up in some Hitachi and Toshiba sets soon if they haven't already.
Of course, these are all 2009 models, which are disappearing fast. (Best Buy discontinued the L37X1, and Sears won't even accept orders for the L37S1 in my area.) The L37S1 is one of the best in this bunch, and I don't see anything in the currently announced Panasonic 2010 lineup that matches it closely.
Good luck, folks!