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