The New York-London Telectroscope
Basically <a href="http://gothamist.com/2008/05/15/telectroscope_b.php">nothing more than a giant webcam</a>, but pretty cool the way they did it up and made it part of the 125th Brooklyn Bridge anniversary:
<img src="http://gothamist.com/attachments/nyc_arts_john/052708telectroscope1.jpg">
<img src="http://gothamist.com/attachments/nyc_arts_john/052708telectroscope1.jpg">