Overview of Online Learning Opportunities

These resources aren't topic-specific, and they're incredibly comprehensive. They're a good place to start for any subject.

The Mason OER MetafinderThe Mason OER Metafinder helps you find open educational materials with a search across 21 different sources of open educational sites.
Free Ebook FoundationHome to more than 100 free science books and more than 2,000 free programming books
Directory of Open Access BooksHome to more than 30,000 academic open-access peer-reviewed books, though it can be slightly overwhelming to navigate
Awesome ListsSort of like a clickable Wikipedia, linking to almost every learning resource with just a few clicks
Wikipedia List of Digital Library ProjectsA list of online bodies of knowledge
Wikipedia's Psychology and Neuroscience categoriesA starting point for everything on Wikipedia about psychology and neuroscience