Since the emergence of Google Maps giving us the ability to put an interactive map on your own web page(s), there are now four separate APIs to choose from: Google Maps, Yahoo! Maps, Microsoft Virtual Earth and MapQuest. These APIs are similar, so once you understand one; it is just a matter of learning the differences of the others.
To get you started, I created four separate maps using each one of the APIs. For comparison purposes, I used the same location points and functional code to create each map, so the only difference is the implementation of the API themselves.
There actually is another mapping API called Map24, but requires that the browser have the Java Runtime installed.
Google Maps: example code documentation official blog
Yahoo! Maps: example code documentation official blog
Virtual Earth: example code documentation official blog
MapQuest: example code documentation official blog