8. Crow Plank
This one is NOT for beginners. The crow plank (eka pada bakasana) is done with elbows slightly bent, one knee in crow, the other leg straight back, floating. With your weight balanced on your hands, bring up one knee then the other and brace them slightly about your elbows. Still with us? Now lift one leg and extend it out and up. Truthfully, if you can do this one, your abs are already rock hard.