Babylon (claims to translate 75 languages to any language from any language. NOTE: the site will try to sell you a paid version. If you do not wish to buy it, you can still use the boxes on this page to do translations). http://www.translation.babylon.com/
Dictionaries.com (includes those languages listed for SDL and Wordlingo, and some European languages they don't have, PLUS: Afrikaans, Filipino, Haitian Creole, Icelandic, Indonesian, Irish, Malay, Maltese, Swahili, Tagalog, Welsh, Yiddish, etc.) http://translate.reference.com/ (of all those I have tried, this seemed to give the best results in German to English — really very good).
Google translate (the only one that seems to include Latin! It has all of those listed under Dictionaries.com PLUS Azerbaijani, Basque, Belarusian, Bengali, Gujarati, Kannada, Persian, Tamil and Telegu, among others.)
imTranslator (a large language list comparable with Dictionaries.com) http://www.imtranslator.net/translation/
Promt (sic) Online (translates to and from most European languages plus Arabic, Hindi) http://translation2.paralink.com/ (of all those I have tried, this seemed to give the best results in French to English translations, of all those listed).
SDL Free Translation (will detect language if you don't know what it is, also translates to and from most European languages plus Hebrew, Turkish, Arabic, Pashto, Urdu, Hindi, Chinese, Korean, Japanese, and Thai) http://www.freetranslation.com/
Worldlingo (similar range to SDL, including detection) http://worldlingo.com/en/products_services/worldlingo_translator.html
Yahoo Babelfish (formerly Altavista Babelfish) — English to and from Chinese, Dutch, French, German, Greek, Italian, Japanese, Portuguese, Russian, Spanish, AND French to and from all of those except Chinese, Japanese and Russian. http://babelfish.altavista.com/
If you have positive experience of any other free online translators, or have a comment on any of those above, PLEASE Contact me and share your information with other scholars!