The Apple iHome Media Centre?
More pictures and video can be found elsewhere, however nobody seems to have a back story or to be able to offer any credible evidence that these are shots of a real product. I think we're going to have to write this one off as fake until, or unless, Steve Jobs proves us wrong at MacWorld next week in San Francisco.
Update: Rui Carmo has done an analysis of the image headers and they seem fairly self consistent, if it's a hoax, it's a good one. However, Simon Woodside has done some forensic analysis of the photos and I'd agree they don't seem to hold up to scrutiny.
On the other hand, Robert Cringley has some interesting reasons why even if these photos aren't real, a (very) sub $500 headless iMac could definitely be on the cards.
Update: Steve Jobs' keynote speech at MacWorld did indeed produce a sub $500 Mac, but it was the Mac mini not the rumoured iHome (above) that was finally unveiled.