Jsconverter is a project mainly written in JavaScript, it's free.
Google Extension for coordinate conversion
Converter Extension for Google Chrome.
Extension helps to convert main coordinate types:
40:26:46N,79:56:55W 40:26:46.302N 79:56:55.903W 40°26′47″N 79°58′36″W 40d 26′ 47″ N 79d 58′ 36″ W 40.446195N 79.948862W 40.446195, -79.948862 40° 26.7717, -79° 56.93172
Uses main coordinate notations from Wikipedia: http://en.wikipedia.org/wiki/Geographic_coordinate_conversion