Geo-Names provides free geo-data such as geographical names and postal codes. The database contains over 6 million entries for geographical names and the whereof 2.2 million cities and villages worldwide. The service can be accessed through an webservice API or you can download and use their data to host on your own database server.
The GeoRSS Google Maps API Extention is a simple way to create a Google Map using the GeoRSS extension to the RSS standard. The API extension is simply a small JavaScript library and is very easy to implement.
The most recent short book release by Pragmatic Programmers is titled - Google Maps and Ajax. It outlines and explains how to hookup Google Maps, Geo Coding and AJAX to create a simple mashup.
Looking to include geo mapping capabilities to your PHP applications? Phoogle Maps is a complete mapping class for Google Maps that allows you to place maps on your page with about 5 lines of code!
I checked out Yahoo! Maps and overall I was very impressed. Although at times the service was slow (but hey, it is just an early beta), the widget that allows you to see your location in a larger context I found extremely usefull for navigation.
The nicest feature though, is the fact that Yahoo! has opened up an API for GeoCoding that uses a simple REST based protocol. If you would like to try the API from PHP, a great example is available at Rasmus’ Toys Page.
