Resources

Games

Chat Noir - Trap the cat! My post
Untangle - Untangle a geometric graph! My post

Math

Estimation 180 - Questions to get students to make estimation
Math Arguments 180 - Pictures for discussion in math class.
Talking Math with Kids - Conversations are great teaching tools.
Visual Patterns - Derive an equation for the visual pattern given.
Would You Rather? - Questions to get students to justify their choices.

History

Mathematical Treasures - Historical mathematical materials, including texts, documents, and artifacts from the collections of David Eugene Smith and George Arthur Plimpton.

Resource

Euclid's Elements - Interactive Euclid's Elements by D.E. Joyce of Clark University.
Math Forum Problem of the Week - Weekly problems and archive.
NRICH - NRICH is a team of qualified teachers who are also practitioners in RICH mathematical thinking. This unique blend means that NRICH is ideally placed to offer advice and support to both teachers and learners of mathematics.
Math Puzzle - Awesome math puzzles. No RSS (AFAIK) so you'll just have to visit the site.
Using GeoGebra on Scoop It! - List of resources on using GeoGebra.
Yummy Math - The site has many current events inspired math activities/investigations. The tagline is: We provide teachers and students with mathematics relevant to our world today ... and it's delicious.

Haskell

Learn You a Haskell - Learn Haskell for fun or for use a an exploration tool in class.

Math Ed

CME Project - Presentation and publications.

Music

Theta Music - Music and ear training games.

Programming

Codingbat - CodingBat is a free site of live coding problems to build coding skill in Java, and now in Python. The coding problems give immediate feedback, so it's an opportunity to practice and solidify understanding of the concepts. The problems could be used as homework, or for self-study practice, or in a lab, or as live lecture examples.
Google Python Class - This is a free class for people with a little bit of programming experience who want to learn Python. The class includes written materials, lecture videos, and lots of code exercises to practice Python coding.

Software Engineering

Stanford

Machine Learning
Introduction to Artificial Intelligence
Introduction to Databases

Science

Biology

The Unofficial Stephen Jay Gould Archive - Collection of articles by the late Stephen Jay Gould.
Google Body - Uses webGL to visualize human anatomy. Can examine at different layers.

Periodic Table of Elements

canvasmol - HTML5 based period table. Visualizes molecules.
ptable.com - Dynamic periodic table. Be sure to check out the states of matter at different temperatures.
periodictable.com - Includes photos of elements.

Physics

PhET - Extensive collection of physics simulation applets.

Video

Teaching Channel - The tag line is "Inspired Teaching, Inspiring Classroom."
Utubersity - Lectures and documentaries
YouTube Education - Educational videos organized
YouTube Teachers - Learn, Teach, Share