iKnow! appears to have the potential to be one of the best online sites for English language learning out there.
Mashable posted about it today, and you might want to read what they wrote.
iKnow! is free, and offers various learning strategies with a lot of audio support. Their “learning English with English support” is fairly limited right now — it’s presently focused on English-to-Japanese and Japanese-to-English — but there is some good stuff for advanced English Language Learners. Once they beef-up that section this site is going to be a real winner and probably a student and teacher favorite.