An excellent iPhone OpenGL ES animation tutorial has been created by Jeff LaMarche covering the concepts of keyframing, interpolation, and creating a looping animation in OpenGL ES.
In the tutorial Jeff uses a simple 3D ball model created in Blender and exported using a custom script (available on the samepage) and goes into great deal explaining the entire process.
You can find the tutorial here along with all the neccessary files including the Blender 3D model exporting script here:
Fundamentals of Animation and Keyframe Animation
I really like this tutorial as Jeff uses the simplest techniques, and explains them in a very straightforward fashion.
It’s good stuff.