OpenGL Demos
OpenGL Misc
MSG Board
Megabyte Softworks
C++, OpenGL, Algorithms

Here is a list of other interesting websites, that deal with programming:

nehe.gamedev.net NeHe was one of the best sources for OpenGL I have found. I started learning from these tutorials. But it's too old today, because these tutorials teach fixed OpenGL functionality, which is deprecated nowadays. But it's not bad to have a look at it. There are 48 tutorials now from basic techniques to some more advanced graphic effects.
www.gametutorials.com Another perfect website for tutorials. There are OpenGL, DirectX, C++, Java, C# tutorials.
www.gamedev.net Game development website. There are lots of articles dealing with game programming. There is also a forum and large programmers community, you can share your knowledge with or seek help with your game development problems.
www.codesampler.com Another excellent site for graphics tutorials.
nehe.ceske-hry.cz NeHe tutorials translated to Czech language.
www.seventhtear.com Programmer from Poland.