Getty Thesaurus of Geographic Names Online is a really complete database of cities, regions, landmarks, etc. which gives their Lat/Lon, historical and modern significance and a bunch of other information. However, it's not really useable in an application as there is too much interface and would require 'scraping' - which I find distasteful.

Maps & Tools has a TON of map locations & other tools. May be nice for finding maps.

I forgot to mention before that the Geospatial Intelligence Agency has the GEOnet Names Server. This includes textfiles of all world cities and regions and geographic information.