Updated roughly monthly, but the download link will always grab the latest version.
"In practical terms, Yahoo! GeoPlanet is a resource for managing all geo-permanent named places on earth. It provides the Geographic Developer Community with the vocabulary and grammar to describe the world's geography in an unequivocal, permanent, and language-neutral manner, and is designed to facilitate spatial interoperability and geographic discovery. Developers looking to geo-enable their applications can use GeoPlanet to traverse the spatial hierarchy, identify the geography relevant to their users and their business, and in turn, unambiguously geotag, geotarget, and geolocate data across the Web."
Note that this dataset does not include coordinate information associated with placenames - only their WOEIDs and some "adjacency relations" allowing one to walk up and down a hierarchy of containing places.
