This list aims to help you choose the right music theory website which comprehensively covers music theory and is 100% free:

1. MTSchools – All aspects of music theory

2. musictheory.net – A flash based site with lessons and exercises

3. teoria - Music theory tutorials, exercises, reference, and articles

4. Music Theory for Musicians and Normal People – An illustrated approach to learning music theory. Some great resources here

5. Music Theory Blog – Lots of music theory topics which are easily accessible

6. music theory for musicians.com – Covers basic to intermediate music theory

7. Dolmetsch Online – A great website covering music theory, music history, and a whole lot more

8. Music Theory Videos – A video approach to learning music theory

9. Open Music Theory – Basic to advance music theory

10. Music Theory - Wikipedia – This should not be excluded from the list as it’s quite informational

If you feel this list is incorrect or should be amended, please comment below.

Happy learning!
Last edited by dhanifrohling at Jan 17, 2016,
Certainly a good list, but I also wanted to include John Oswin's music theory series on YouTube. He is a spectacularly good teacher. Don't be put off by the sheer number of videos (around 40). They're well-paced and John's sense of humor makes learning fun. I learned way more about music theory from John Oswin's videos than from every other resource put together.