Making a quick dump of links, I'll make this pretty later.https://gumroad.com/l/OizvO
165 minutes painting - Space Salvage
30 minute painting - Desert runner
Art Pack 1 - Brushes and shapes for Photoshop
Art Pack 2 - Tool Presets and Brushes for Photoshop
Accuracy - A Drawing Guide by Dorian Iten
Focus: Proper Proportions/Measuring
Price: Pay what you want.
Description: Great for beginners, or people who may not have learned some of the foundations of measuring in school. This teaches the basic methods of comparing angles, lines, and analyzing shapes.