Google maps

http://abduzeedo.com/clever-google-maps-manipulations-christoph-niemann Clever art drawn in the style of Google Maps. I think this really shows off how well-made the Google Maps design language is.

http://www.flightradar24.com/ See flights in real-time from everywhere around the world.

http://www.pubcats.com/catmap Find the nearest pub with a cat!

http://www.mapstd.com/ MapsTD is a tower defense game with maps dynamically generated from Google Maps locations.

http://extendny.com/ The New York City grid extended to the entire planet.

http://traintimes.org.uk/map/tube/ Watch the location of London Underground trains in real time!

http://www.n2yo.com/ LIVE REAL TIME SATELLITE TRACKING with Google maps.

4/8/07 Gil's LotD
http://hotcaptcha.com/ This website will show you three women (or you can choose men) from AmIHotOrNot.com and you need to choose the three who are hot. It's one hypothetical way of stopping spambots.
http://googlesightseeing.com/maps?p=1123&c=&t=k&hl=en&ll=53.641719,-1.951522&z=17 A house stuck right in the middle of a highway.

Gil's LotD
http://www.ahding.com/cheapgas/ Using Google maps to find cheap gas