I recently started watching the Blender Foundation Humane Rigging DVD by Nathan Vegdahl, and I'm about halfway through it. The DVD¹ is great, but it doesn't really have anything to do with iOS or graphics programming.
Sometimes, however, you find amazing things in unlikely places, and this is one of those times.
If you're interested in learning or getting better at rigging 3d models for animation, especially using Blender, you absolutely should pick up this video. It's one of the best pieces of Blender-related pedagogy that I've seen. In fact, it's one of the best training videos of any kind that I've ever watched. It does a tremendous job of breaking down complex concepts and focuses on teaching the why as much as, if not more than, the how. You walk away not just knowing how to build a rig: You walk away knowing how to build nearly any rig you might need.
But even if you don't give a rat's ass about Blender or rigging, you might want to check this DVD out anyway. The reason for that is the third chapter. If you've ever had trouble with some of the basic 3D concepts like axis-angle rotation, Euler angles, gimbal lock, or just what the hell these quaternion things are, you should watch Chapter 3 and just ignore the Blender-specific parts. If you're not interested in learning rigging, you can skip the last video in the chapter that applies what's been learned to Blender. The rest of the chapter is almost all theory and concepts, and it's brilliant.
I can almost guarantee that you'll walk away with a solid understanding of the what and why of these foundational concepts, and that will help with any graphics programming you might be wanting to do, whether it's OpenGL ES, Unity3D, Cocos3D, or whatever.
I would strongly encourage you to buy the DVD if you're interested in the video, but it was released under a Creative Commons Attribution license, so you can torrent it legally and mostly guilt-free. Throwing a little money at the Blender Foundation will result in good karma, though.
1. This is a data DVD of video files, not a video DVD you watch on a DVD player.