thespacegoat:

Courses:
Coursera
EDX
Udacity
University of Reddit

Books:
Bartleby
Gutenberg
Librivox
Poem Hunter

Videos:
Academic Earth
C. G. P. Grey
Crash Course
Khan Academy
Minute Physics
The New Boston Tutorials
TED
Unplug the TV

Documentaries:
Documentary Heaven
Top Documentary Films

Languages:
BBC Languages
Busuu
Dou Lingo
Live Mocha
MemRise
Verbling

Music:
How to Play Piano
Justin Guitar
Music Theory
Play Bass Now
Teoria

Programming:
Code Academy
Coding Bat
HTML Dog
Learn Code the Hard Way
Ruby Monk
Trypython

DIY/How-To:
Howcast
How Stuff Works
Instructables
The Daily Miscellany
Wiki How
Wonder How-To

Math:
Math Run
Project Euler
Wolfram Alpha

Cooking:
Cooking for Engineers
Cooklet
How2Heroes
Reluctant Gormet