An online GLSL shader editor with the option to provide custom uniform variables and upload own 3D meshes.
Shdr is a live ESSL (GLSL) shader editor, viewer and validator powered by WebGL and built by Thibaut Despoulain (BKcore).
Learn OpenGL . com provides good and clear modern 3.3+ OpenGL tutorials with clear examples. A great resource to learn modern OpenGL aimed at beginners.