How to spend my summer improving my programming skills?

I am a belgian computer science student and will finish my bachelor next year. I would love to spend my summer in California to expand my knowledge of computer science and to experience the atmosphere of Silicon Valley.

The biggest project I co-created untill now is an Android app equivalent to Blackboard Mobile. We worked on that with six people, as a task for the university. So I'm not a very experienced programmer yet. But because I follow all the tech news everyday, my knowledge of the market is up to date.

Most of the university summer courses seem to be for high school kids, but after two years of study I think that won't be challenging enough. There is one course at Stanford ('Client-Side internet technologies') that seems perfect for me, but it already starts in June, when I still have exams in Belgium. I will be able to stay in California from mid July untill mid August. I would also be glad to take some language courses, in preparation for my GRE. Do you guys know of any courses that might suit me?

As mentioned before, I'm not very experienced yet. But if you know of a stage at a company or a research project that might suit me, that would be very interesting as well.

Thanks a lot!

Lucas