It may seem strange that the Massachusetts Institute of Technology, an institution better known for number crunching than ab crunching, has put together such a nice, comprehensive outline of stretching techniques, but they have.
Though it doesn’t include photos or diagrams, “STRETCHING AND FLEXIBILITY: Everything you never wanted to know” by Brad Appleton, is about as comprehensive a list of flexibility exercises as you would ever want to see.
You can reference it here.
Learn more about the bellicon and flexibility!