Khan Academy - a library of over 2,400 videos covering everything from arithmetic to physics, finance, and history. A mission to help you learn what you want, when you want.
Brain Pickings - "a discovery engine for interestingness, culling and curating cross-disciplinary curiosity-quenchers, and separating the signal from the noise to bring you things you didn’t know you were interested in until you are." One of my favorites.
Big Think - Blogs, articles and videos from the world's top leaders and thinkers.
Thinking Allowed - provides an open, non-adversarial forum for the exchange of intelligent, alternative ideas.
TWM Reference Index - a variety of interesting and mentally stirring articles about science, consciousness, and anthropology.
RSAnimate - Dozens of insightful talks by leading scientists and scholars in their fields drawn real-time on a white board. Awesome for visual learners.
Compassion Pit - This one's cool. Choose to be either a venter or a listener, and participate in an interaction with another person in that role. This is an enlightening way to improve your listening skills, or to get something off your chest!
Heavy Petal - How to make seedballs, or flowerbombs. Get guerrilla gardening today!