Online resources for second language acquisition:

BBC Languages - Courses and phrases, audio and video, vocabulary, pronunciation, grammar, activities and tests

DUO Lingo - Duolingo offers courses in:  Spanish, French, German, Portuguese, Italian

Lingro - remembers all the words you look up, so you can easily review and study them. 

Dave's ESL Cafe - 

Quizlet - We make simple tools that let you study anything, for free.

LiveMocha - Learn to actually speak a new language (or two). Trust us – you can do it!

Busuu - Learn languages online with interactive language courses and lessons

Glossary of Second and Primary Language Acquisition Terms  

Free Online Language Courses

Daniel Tammet's website