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