A couple of people emailed me asking if I knew of a specialized database where they could download (for free) high-quality satellite and aerial imagery. The answer is yes.
You'll notice with MSN Virtual Earth that much of the imagery comes from the U.S. Geological Survey (USGS). If you're interested in downloading some of this material as TIFF files, go to: http://seamless.usgs.gov.
Spend some time reading the documentation. This is a powerful resource if you spend some time learning how to use it. You'll also see that Seamless.usgs provides some access to non-U.S. imagery. Remember, the imagery that's available for one location might now be available for another. "Seamless" also allows you to overlay data on top of images.
TerraServer-USA from Microsoft has been around for years and also provides access to much of the same imagery that's now available from MSN Virtual Earth. Each entry also contains the data the image was taken.
TerraServer offers direct links (when available) to high-quality images, aerial images, and topographic maps. Images are available in three sizes. You can also print, e-mail, and/or save imagery to your computer. Links at the bottom of each page provide access to basic demographic data about the area you're looking at. It's potentially useful stuff for the web researcher. It's one thing to see an aerial image but knowing about what you're looking at makes the service even cooler and more useful.
However, what TerraServer-USA offers in terms of data is just the tip of the iceberg. If detailed information about the specific area you're viewing is of interest, I suggest taking a look at a free service called TerraFly. I've blogged about it before.
What makes TerraFly different than other services is the amazing amount of textual data it offers.
To access, simply click a spot on the aerial image. A new window will open containing census info, a list of streets, local business names, recent fires, weather, etc. If you click on another location, even a few blocks away, you'll likely get different information. This "experimental" page offers even more data.