Google Earth combines satellite imagery, maps and the power of Google Search to put the world's geographic information at your fingertips. (Free—and for now only runs on PCs, though a Mac version is in the works.)
Google Earth Community
The Google Earth Community overlay has Wikipedia-style notes on interesting buildings and historic sites.
MSN Virtual Earth
Provides directions, interactive maps, and satellite/aerial imagery of the United States. Can also search by keyword such as type of business. [For some parts of the U.S. has superior photos, lacks the flying and 3D features.]
A blog about the wonderful things being done with Google Earth.
Google Earth Blog
All about Google Earth... ... This blog is dedicated to Google Earth (GE) news, features, tips, and applications.
Flight tracking, flight planning, flight plan filing, aircraft scheduling, pilot's logbook. Useful site for pilots, FBOs and aviation-related companies. Offers a limited free demonstration of a for-pay service, showing the tracks airliners are taking toward particular airports. the free sample colvers LAX airport, and by using the tilted view you can 'watch' planes as they descend through the Los Angeles basin for landing.
Blogwise - Blog directory
A directory of blogs, grouped by keyword and country. Intends to be a guide to blogs around the world.
Photo-sharing site run by Yahoo. Hundreds of millions of photos have been stored at Flicker, many of them manually tagged by location or otherwise 'geotagged' with GPS coordinates. With the Flickr overlay turned on, you see any available photos of the place you're looking at.
A California softward firm which dominates the world market for "geographic information systems," a sophisticated and high-priced counterpart to Google Earth's overlays.