google maps API
The google maps API is now "official." I tried it out; it is incredibly easy to use. It took about 20 minutes for me to make a nice map on my wife's web site. I could do it again (now that I understand the API) in about 3 minutes.
There is one serious problem, and that is their API access key system. It is incredibly brittle, and can cause your maps to work on "www.example.com" and fail on "example.com." And randomly work or break on funny hosts like http://test.example.com:8080/.
Hopefully google will fix this soon or just disable the API key thing until they can.