Mapstraction - A Javascript Mapping Abstraction library

Mapstraction is a library that provides a common API for various javascript mapping APIs to enable switching from one to another as smoothly as possible. Developers can code their applications once, and then easily switch mapping provider based on project needs, terms and conditions, and new functionality.
It currently supports Cartociudad, Cloudmade, GeoCommons, Google Maps & Google Earth, Leaflet, MapQuest, Microsoft, OpenLayers, OpenSpace, Ovi, Yahoo and Yandex.