Bookcrossing
Read and release your books into the wild! tag your used books with a unique tracking number, then follow their travels through the world at bookcrossing, the world's biggest book club.
http://www.bookcrossing.com/
Confluence
The degree confluence project contains photographs of the intersections of integer latitude and longitude degree lines.
http://www.confluence.org/
Geocoins
Geocoins
http://www.geocoins.ca/
Groundspeak
Groundspeak
http://www.groundspeak.com/
Minutewar
Minutewar.org
http://minutewar.org/
Treasureclub
Treasureclub
http://www.treasureclub.net/