For sure Pothead is a great SubD tutorial that teaches lots of good topology.
https://cgcookie.com/courses/pothead-create-a-hard-surface-character-in-blender
You can also watch the old Mesh Modeling Bootcamp, which has golden knowledge for the ages, no matter the Blender version:
https://cgcookie.com/courses/blender-mesh-modeling-bootcamp
Also the sci-fi helmet is a great one, so you’re on the right path.
