Math

Learning How to Learn - start out by learning how to learn effectively (and how to have more fun doing so) – https://www.coursera.org/course/learning

Khan Academy - an extensive and pedagogically excellent resource on almost anything math – https://www.khanacademy.org/

Wolfram Alpha – a stunning resource for exploring math interactively – http://www.wolframalpha.com/

Sage – a popular, open source CAS – http://www.sagemath.org/

SageMathCloud - a web-based interface to the Sage – https://cloud.sagemath.com/