The web is full of great sites, here are some of my favourites.

Games Development

Simon Schreibt
Breakdowns of tricks, tips and techniques used by games developers (art focused).
Fabien Sanglard
Very insightful code reviews of open source software.
Mr. F/ndotl
Great graphics demos.
Íñigo Quílez
Awesome fractals and CGI.


As many "two-triangles" shaders as you can view!
GLSL Sandbox
WARNING: OFTEN NOT SAFE FOR WORK. An anonymous "two-triangles" gallery. Users frequently "fork" one anothers' shaders, creating variations on them.