There is no single best source. Many of the standard universities have .edu sites that provide a lot of information. There are lots of online courses on iTunes University.
Google will provide you with more garbage than gold. It's up to you to sort it all out, and the only way to really do that is to understand what you're reading. And amidst all the crackpot theories and insanity, you may find it more than you can absorb. Eventually you have to start selecting resources/people that you trust for information in order to reduce the amount of data you have to sift through.