I'm in a rush to get to the library today, but before I go, I have to give a shout-out to Google Sightseeing, a really fun site for fans of travel, architecture and geography. The site has found a fun use for Google Maps' new satellite-image feature. Now when people say, "This is so huge, it's probably visible from space," you can check up on their conjectures and maybe even submit an item to the site. One of my favorites is the Unisphere from the World's Fair. Other notables are Flock of Birds and UFO! It all sort of reminds me a bit of SimCity (without Godzilla of course).
The only problem is, I don't know how often these images are updated, so you're working with a fixed point in time (whenever the satellite happened to be shooting that part of the country).