Seiki do a 50 inch one that can be obtained for around $1000 US at the moment
I was about to question whether or not the monitor would actually accept a 4k signal from a computer (rather than just taking a 1080p signal and upscaling it).
But then I saw one of the review/comments to the Amazon entry which included the exact commands required to get the thing to display a computer image at 4k. Pretty cool.
And of course, my current cad box has a total of eight video outputs, so I could have one of these plugged into the port capable of 4k output, and still have seven of my eight dell 2407s connected at the same time.
Imagine what a flight simulator would be like with eight of these things. :-)
(Is there a such thing as a video card which can do eight 4K outputs at any sort of a decent frame rate?)