What is a good ESL learning site?

Are there any sites out there that have English flashcards with pictures and audio? Most of the ones I found were printable, but I think my son would benefit from online tutorials and lessons so he can work on it on his own time. He is learning English as a second language and is motivated to learn, but sometimes when he is reviewing by himself, he is mispronouncing words. Hearing the audio would be a big plus. Thanks!