BabelFish Instant Translation plugin for Firefox. Uses proprietary web services to actually do the translation, but it provides a good interface for looking up words from a web page. Maybe some day we can provide our own translation web service, whether it is edited by humans or assembled as a result of machine learning. (Actually, building such services is probably beyond the scope of Wikiotics, but it would be nice if they existed anyway.)
Foreign Service Language Classes Has many language lessons developed by the US Government, and thus in the public domain. These are full introductory circuli for many languages.