I present to you Project Blinkenlights, probably one of the coolest things I have ever seen.
People familiar with the CCC (Chaos Computer Club), which I guess outside Germany are not that many, and Tim Pritlove should know about this, but I think most of you don't, so I really think this deserves to be on Teamliquid. TL is all about awesomeness after all
They basically take a building and turn the windows into computer screen pixels (and allow people to play games on it among other things). With each project it gets more and more awesome, so far they have done three installations. The first one in Berlin in 2001-02 (which they repeated a few times in the same way). The other two were part of Nuit Blanche events (all night cultural events) in Paris and Toronto respectively.
I don't wanna talk about it too much, since I'm rather lazy, so I'm just going to provide you with videos and pictures:
First installation, 2001, Berlin: Blinkenlights
Second installation, 2002, Paris: Blinkenlights Arcade
Third installation, 2008, Toronto: Blinkenlights Stereoscope
Tim Pritlove, one of the heads behind it, also did an hour long presentation at the Chaos Communication Congress in December 2008 (the third video from above is part of the presentation if I remember correctly), with loads of background information and how everything works. Really interesting! You can watch it here. The embedded video is apparently not seekable (at least it isn't for me), but they also offer it as a direct download which is seekable.