A client needed a web application with, among other features, geocoding—given an arbitrary string specifying a location anywhere in the world, find the latitude and longitude of that location. Google and Bing seem to have the best APIs for this, for the following reasons:

• Global. Other APIs provide geocoding only of US addresses.
• Parses the query string you provide. Other APIs require you to parse out country, address, postal code, etc. Bing actually allows both types of queries.
• Web-based. Other APIs require downloaded software to be integrated into your application. Google and Bing support XML "Web Services" and JSON RESTful APIs

Other services I considered:

• Caspio is interesting, but not really an API. Rather, they add latitude/longitude columns to locations entered into your Caspio database.
• DOTS Address Geocoding provides US addresses only. Also, you must parse out the city, state, and postal code.
• Pitney Bowes appears not to have a web based service (except for trial testing). Also, you must parse out the city, state, and postal code.
• Melissa DATA works for US addresses only, and requires a specific format including address, city, and state.
• Yahoo! has a RESTful API that allows entry of free text, but it must be in a specific format.