I highly recommend ICLS.

I highly recommend ICLS.
When I moved to the US, I couldn't understand when people were talking to me. Now, after a few months in their Intensive Course, I can speak comfortably in any situation.
They offer free extra activities such as conversational groups and field trips to museums and galleries in DC, wich is ideal for making friends with students of other levels, who come from many countries around the world.