A real-time map of all the trains on London Underground, created by Matthew Somerville at the Science Hackday.
I could look at this all day, as the little icons move through parks and along roads. (Obviously I can't look at it all day, because I've got other things to do...)
It's like a toy train layout, only it's real, and it covers the whole of London Underground. And when you click on each train it tells you its details.
The whole thing is created from information that TfL already had, but weren't using for the public good. I can't decide whether it's art or science.
Thanks to Luke and Phil for sharing this. I wish I could get everyone to look at it.