By CKR
These two sites provide a wealth of information presented as maps. One caution, though. You can get to some pretty pictures fairly easily at both, but both are so rich that you should plan to spend some time with them if you want to use them in any depth. Both sites allow you to build your own maps with the data you want.
Geodata.gov contains mappable data from the federal government. Many agencies have contributed, so you can find anything from physical and political maps to geological, ecological, and climatic data to utilities and transportation networks.
The Jules Map Server provides information on Earth and the planets out to Jupiter, along with their moons. You need Java to access all the site's features. This image is from Jules.