I like to keep everything on the character without messing too much with sliding numbers in tiny boxes. That way the animator can quickly experiment with poses and get organic shapes.
Here is the setup I came up with:
Variable foot from Armin Halac on Vimeo.
As seen in the video the foot is really flexible and allows for easy posing. The bend control can moved to any point along the foot and make the foot bend in any direction. The only slider that requires the animator to take his/hers eyes of the character is used to control the falloff. Falloff control allows the foot to peel nicely from the ground or to bend at a harsh angle. The foot uses the same rig for both IK and FK modes.
The model is owned by Irie Studios.