There's some great stuff over on We Make Money Not Art this morning. Aside from the previously mentioned coffee mouse, they also feature the Timescope.

Mounted on a Berlin rooftop, the Timescope functions like a regular rooftop telescope, except images from vintage photographs of the Berlin cityscape are fed into the digital viewfinder. The Timescope has internal sensors that determine which angle of the city you are viewing and adjusts the display to match. I'm guessing it could be set up with a trackwheel to scroll through the years as well, assuming enough photographs could be sourced.

They should put one of these on top of the Empire State Building, it'd be amazing.