Beginner
HTML Best Practices (github.com)
HTML Content (www.codecademy.com)
Learn HTML (www.codecademy.com)
Learn HTML in 12 Minutes (www.youtube.com)
Front End Interview Handbook (github.com)
HTML Fundamentals (www.codecademy.com)
Marksheet (marksheet.io)
Organizing HTML & CSS (www.codecademy.com)
HTML Beginner Tutorial (htmldog.com)
w3schools (www.w3schools.com)
How to Use the HTML5 Sectioning Elements (blog.teamtreehouse.com)
Intermediate
HTML Intermediate Tutorial (htmldog.com)
Advanced
HTML Advanced Tutorial (htmldog.com)