GLee (GL Easy Extension library) is a free cross-platform extension loading library for OpenGL. It provides seamless support for OpenGL functions up to version 3.0 and nearly 400 extensions. GLee is distributed under a modified BSD license.
Super easy to integrate into your project. Drop in GLee.c, include "GLee.h", then go to town. It has been very useful, but the newest version is currently languishing in SVN. Make a release!