Where you go to college and the amount of any scholarships you get are a bigger deal for your long term personal growth than any of the specific subjects you will learn right now.
In the spirit of long term decision making, figure out where you want to go to college, or what your options are, and spend the summer maximizing the odds of getting in to your first choice schools. I cannot imagine that it won't be a better investment of your time than any one subject you are studying (unless you are preparing for SAT or some such test.) So I guess you should spend the summer on Khan, and learning and practicing vocabulary to get better at taking the tests that will get you into a great college, where your opportunities to learn are greatly expanded.
I'm afraid all of this is not really applicable to me... My country isn't Western enough for such a wide range of opportunities. Here, institutes for higher education range from almost acceptable (state universities) to degree factories (basically all private colleges). Studying abroad in a Western country costs, per semester, somewhere between half and thrice my parents' yearly income. On top of everything, my grades would have to be impeccable and my performances worthy of national recognition for a foreign college to want me as a student so much as to step over the money issue and cover my whole tuition. (They're not, not by a long shot.)
Thanks for the support, in any case...
If you've recently joined the Less Wrong community, please leave a comment here and introduce yourself. We'd love to know who you are, what you're doing, what you value, how you came to identify as a rationalist or how you found us. You can skip right to that if you like; the rest of this post consists of a few things you might find helpful. More can be found at the FAQ.
A few notes about the site mechanics
A few notes about the community
If English is not your first language, don't let that make you afraid to post or comment. You can get English help on Discussion- or Main-level posts by sending a PM to one of the following users (use the "send message" link on the upper right of their user page). Either put the text of the post in the PM, or just say that you'd like English help and you'll get a response with an email address.
* Normal_Anomaly
* Randaly
* shokwave
* Barry Cotter
A note for theists: you will find the Less Wrong community to be predominantly atheist, though not completely so, and most of us are genuinely respectful of religious people who keep the usual community norms. It's worth saying that we might think religion is off-topic in some places where you think it's on-topic, so be thoughtful about where and how you start explicitly talking about it; some of us are happy to talk about religion, some of us aren't interested. Bear in mind that many of us really, truly have given full consideration to theistic claims and found them to be false, so starting with the most common arguments is pretty likely just to annoy people. Anyhow, it's absolutely OK to mention that you're religious in your welcome post and to invite a discussion there.
A list of some posts that are pretty awesome
I recommend the major sequences to everybody, but I realize how daunting they look at first. So for purposes of immediate gratification, the following posts are particularly interesting/illuminating/provocative and don't require any previous reading:
More suggestions are welcome! Or just check out the top-rated posts from the history of Less Wrong. Most posts at +50 or more are well worth your time.
Welcome to Less Wrong, and we look forward to hearing from you throughout the site.