Art
Perspective
Perspective Wikipedia [Web] (FREE)1 Point Perspective Interactive Lesson [Web] (FREE)
2 Point Perspective [Web] (FREE)
Perspective Detailed discussion [Web] (FREE)
New Perspective System [Book] ($$$)
Color Theory
Color Theory Basics [Web] (FREE)Color Theory Detailed discussion [Web] (FREE)
Colors on the Web [Web] (FREE)
Color Scheme Generator [Web] (FREE)
Color Scheme Tool [Web] (FREE)
Color Theory for Digital Displays [Web] (FREE)
Light & Shading
Anatomy
Z-Anatomy-Z Blender anatomy app [Software] (FREE) (website down )Software
Krita painting app (FREE) [Software Win, mac, Linux] (OSS)Hardware
XPPen Display Tablets [Hardware] ($$$)Wacom [Hardware] ($$$) drawing pen tablet Intuos Medium, bigger isn't better.
Imaginative Realism by James Gurney [Book] ($$$)
Color and Light: A Guide for the Realist Painter by James Gurney [Book] ($$$)
Creative Illustration by Andrew Loomis [Book] ($$$)