The past few days I've been rigging this character. Thankfully, I think I only have to do this one rig, then all of the characters in the game I'm helping make will be able to share this rig and share it's animations, thus saving me a metric shitload of time.
If this rig looks familiar to you, then you probably work at Valve. I "borrowed" their rig to use on this character and studied it's innermost secrets. Appearances can be deceiving though, the only thing I truly "stole" were the fairly generic control curves, which are pretty simple to create. The real meat of this rig I still had to do myself.
I had to resize and reposition all of the curves, redo all the constraints and the set driven keys, and was inspired to write a "ZeroGroup" script by looking at the way all of Valve's control curves were parented under groups to reset their transformation values, something I didn't know about before. I learned tons more by copying their rig's setup as well, using multiple IK handles in the feet to control rotation (which, if you use orient constraints, seems to conflict with the FK orient constraints in strange ways), I learned cool stuff like showing the display handles on the curves to make them easier to select, using empty groups in the feet to set different pivot points.
It's been a pretty great learning experience overall.