Short for Technology Entertainment and Design, TED is a set of annual conferences that brings together some of the world's best and brightest thinkers to deliver talks on their realms of expertise. While tickets to the conference are superscarce — and superpricey — TED gives back by making its archives of TEDTalks available online for free. Some picks: Steve Jobs on "How to Live Before You Die" from 2005, and Elizabeth Gilbert's talk on creativity from 2009. (See the TED Talks mobile app.)
The classics: Wikipedia, Project Gutenberg, How Stuff Works, Instructables, Howcast