There are numerous other resources which can be of tremendous use to both map designers and the consumers of these types of services alike. Some of those resources include:
GeoEye offers effective solutions and decision-support tools for a variety of business, economic, environmental and security challenges around the world. They bring actionable Earth imagery to life, revolutionizing the way they view, map, measure, monitor and manage the world in which we live.
Google Maps is a tremendous resource provides detailed street-level maps and access to free, reasonably-current satellite imagery over a wide area of North America, Europe and other locations.
Google Earth is a stunning collection of satellite imagery and maps covering a broad geographic area. Google Earth also allows users to view at least a handful (for now) of downtown metropolitan areas in oblique views...as well as the overlay and upload of custom-designed graphics from firms such as mapformation, allowing clients to view their property maps in relation to other geospatial information already included within the Google Earth service.
MapQuest is admittedly not our favorite "canned" mapping service on the internet. However, they do generate millions of visits on an annual basis, and our staff does make regular use of their "Driving Directions" feature when planning shortest routes to meetings. 
multimap is Europe's leading provider of mapping and location-based services. Our company delivers more online maps, point-to-point driving directions and geo-spatial ("where's my nearest?") searches to businesses and consumers than any other supplier in Europe.
World Wind lets you zoom from satellite altitude into any place on Earth. Leveraging Landsat satellite imagery and Shuttle Radar Topography Mission data, World Wind lets you experience Earth terrain in visually rich 3D, just as if you were really there.
The TerraServer-USA web site is one of the world's largest online databases, providing free public access to a vast data store of maps and aerial photographs of the United States. TerraServer is designed to work with commonly available computer systems and Web browsers over slow speed communications links.
TopoZone offers one of the most complete set of digital topographic maps, aerial photographs, and related mapping information to the professional and outdoor recreation communities. TopoZone is a production of Maps a la carte, Inc.
Windows Live Local combines mapping and local search to put the answers to your search questions in a geographical context. To do this, Windows Live Local combines MSN Search with the latest in mapping to create a new Web application built on Microsoft technology.
Yahoo Maps (Beta) is very similar to Google Maps with some additional interesting features, such as better detailed satellite imagery in some locations, as well as a Live Traffic feature that estimates vehicular traffic flow within particular regions. The service is still in "beta" mode, but is definitely worth a look!