The current 27" iMac and Thunderbolt display both use an LG IPS panel: the LM270WQ1 which is also used in Dell's UltraSharp U2711 monitor. Dell just announced today that they're replacing their UltraSharp U2711 monitor with the UltraSharp U2713HM, which is their first to use an LG AH-IPS panel. AH-IPS stands for "Advanced High-performance IPS" and should offer significantly better clarity and color accuracy. The Dell UltraSharp U2713HM also offers an impressive dynamic contrast ratio of 2 million:1. Unless Apple plans a radical shift to IGZO for the next iMac refresh, which I doubt since MacBooks/iPhones/iPads would logically be the first targets in order to benefit from IGZO's high energy efficiency, it looks like this AH-IPS LG panel would be the logical choice for the upcoming 2012 27" iMac and Thunderbolt display.