The first is International Business Times. They have fixed the exact moment as 6:12 a.m. EST (New York Time), which is 11:12 a.m. Coordinated Universal Time (UTC).
Just to confirm, we logged in to Time and Date, experts in times and dates. With a full-page countdown clock, they predict the world will end one minute earlier -- at 11:11 a.m. Coordinated Universal Time (UTC) or 6:11 a.m. New York time.
Why the disparity? It turns out that 11:11 was originally determined to be the time of the winter solstice. But the US Naval Observatory changed their website to take account of the latest estimate for leap seconds and the solstice has now been determined to take place at 11:12 UT. (Thanks Bikenbeer2000)
But we're not done. Horoscope.com claims the world will end at 23:11:11 a.m. (EST time)
December212012.com claims it will end at 11:11 UT as well. "There can only be one Official Countdown Timer and we have it," they say.