The following are some some links to sites that can help you better your graphics programming skills.
Don’t just memorize math, understand it!
Great place to practice writing pixel shaders.
Another great place to practice writing pixel shaders. This site also makes it easy to use textures, video, and sound in your shaders.
iñigo quilez’s Homepage
The creator or shadertoy has some really great
articles that will get you up to speed!
Marmoset Toolbag 2 – PBR Theory
Some great info regarding the theory behind Physically Based Rendering.
The Book Of Shaders
Very nice tutorial on how to write fragment shaders.
Great place to learn OpenGL
Useful Web Apps
A no-nonsense very easy to se online graphing calculator.