worldKit Geocoder : free search for latitude/longitude
Enter US street address, zip code, or international city. Or just click on the map.
[Exclude zip for US Street Address. 5 digit US zip, 3/4 digit UK postalcode. Include state for US cities.]
Address geocoding courtsey geocoder.us. US zip code geocoding by Geo::PostalCode. UK postal code geocoding by jibble.org. International geocoding from GEOnet Names Server.
There is a REST interface to the GNS and US city data at http://brainoff.com/geocoder/rest/. Please get in touch if you make use of it.