As the Internet continues to grow, so to does the functionality of mapping applications on the web.  As more and more imagery becomes available to the general public, programmers are finding ways to embed this data into web applications.  Below is a list of sites implementing this new and emerging technology:

http://www.flashearth.com/
Users have an opportunity to view most of the major aerial mapping sites from one flash-enabled interface.

http://terraserver.microsoft.com/
Microsoft site housing aerial photography for most of the United States

http://earthshots.usgs.gov/
USGS Earthshots historical Landsat imagery for selected areas on the planet

http://terralook.cr.usgs.gov/
New historical-vs-current Landsat collection