All Free Dictionaries Project
Online project to build free translating dictionaries (e.g. English to Spanish) by allowing individuals to add and correct entries. Several dozen languages represented so far. Dictionaries can be searched online or downloaded. Includes links to other free dictionary sites.
Extensive site devoted to teaching Esperanto. Many lessons with sound, a library of Esperanto writing, a dictionary for translating Esperanto to/from many other languages, games for practicing vocabulary, forums, and more. Site is available in English and many other languages.