For centuries, ships navigated by the stars. Thousands of ships' logs representing hundreds of thousands of position readings were diligently recorded by sailors for a future use they never could have imagined: 100 years of ocean travel 1750 to 1850.
Google Maps now integrates with Wikipedia (click "More" tab). Concharto is a geographic wiki for documenting historical events. Flick also has a map service.
Breathing Earth. A map of the world showing a real-time simulation of the CO2 emissions level of every country in the world, as well as each countries birth and death rates.
Who'll be living where. Researchers at the Earth Institute at Columbia University have developed map that projects where people will be living in the year 2025.
"Getting There." MapQuest demystified from The New Yorker.
Sea levels are on the rise. Flood Maps mashes up NASA elevation data and Google Maps, and offers a zoomable localized visualization of the effects.
GarbageScout. An interactive online map for locating and posting free stuff that's lying around your neighborhood.
The Barrington Atlas of the Greek and Roman World provides beautiful detailed topographical maps of the ancient world. A mammoth undertaking in production over 12 years with 160 scholars and cartographers (with help from MapQuest) and estimated to cost over $5 million it is the largest and most accurate Ancient World Atlas ever. Composed of 99 maps (examples) the Atlas is easily available to the layperson. "If you're gripped by Hannibal and want to sort out which way you think he went through the Alps, you'll have enough of a clear landscape to do it. If you want to follow St. Paul around the eastern Mediterranean, you can."
A bunch of very beautiful Old Japanese Maps has been put online. Java application Insight(tm) required to view and includes a nifty GIS application to overlay old maps on current maps with 3-D animated fly-throughs. State of the art in online map presentation "The digital images are even better than the originals because you can amplify them, rotate them to look at them from different angles," Mr. Zhou said. "In practical terms, this is a better way of using the material than actually coming here to see the pieces."