3840 x 2160 - $449 at Amazon at the moment - http://www.amazon.com/dp/B00DOPGO2G/
Amazing price. Dunno how good it is.
There's a 50 inch version too, for $649. But since there's almost no "4K" content out there, it seems silly to be an early-adopter to use one as a TV now. And who has a desk big enough to use a 50 inch monitor?
Cheers,
Scott.