The USGS (U.S. Geological Survey) has an online satellite image viewer called The National Map. See an aerial view of your own house, and maybe even your car, if you were home that day. You can overlay map info, topographical info, and several different satellite images all together.
TerraServer is another site that has 3.5 terabytes of satellite images of the U.S. and Europe.
The US Census Bureau has searchable street maps and census statistics (1990) for any area in the country. The maps are detailed enough to contain every street, but aren't labelled except for city names and political boundaries.
The Perry-Castañeda Library Map Collection has a large set of world, continent, and city maps. They also have US historical maps. These maps are labelled better than the Census Bureau maps, but aren't as detailed.
Find the latitude and longitude of any address with the Eagle Geocoder.
Find the distance between any two places with the "How far is it?" page provided by Bali Online.
Compare U.S. states' sizes and populations.
Airlines: AirTran, American, America West, Continental, Delta, Northwest, Southwest, TWA, United, US Airways.
Track a flight in progress on the USAToday site.
Compare flight information:
Traffic: SmarTraveler provides up-to-the-minute traffic information for eleven major metro areas, and it's surprisingly detailed.