Mapping APIs

Some interesting Mapping API found on stack Overflow

Geonames
The GeoNames geographical database is available for download free of charge under a creative commons attribution license. It contains over eight million geographical names and consists of 6.5 million unique features whereof 2.2 million populated places and 1.8 million alternate names. All features are categorized into one out of nine feature classes and further subcategorized into one out of 645 feature codes. (more statistics ...).
The data is accessible free of charge through a number of webservices and a daily database export. GeoNames is already serving up to over 11 million web service requests per day.

WCF example from CodeProject: GeoNames .NET WCF Client

Topocoding

This service is an extension of existing mapping APIs in Javascript. It serves for querying the altitude information
and other topological information about places on the Earth.

The topo data is a combination of SRTM and GTOPO30, its typical horizontal resolution is about 90 meters. The data includes all continents but Antarctica.

Currently the service is in the beta stage of testing, the throughput of the shared server might be limited.
For business users, we offer paid servers with dedicated capacity.

EarthTools.org

Here's a collection of webservices for finding out geographical-related information. There are currently three services available for finding the time zone or local time, the sunrise and sunset times, and the elevation/height above sea level at a given latitude and longitude.