One of the powerlifters in our gym came up with a good one. He made this wheel set up that you put on your feet. This is for trunk training and it works. You put your feet in the stirrups, lay out flat supporting your upper body push up style, point your feet towards your head, and walk on your hands.
He has come up with some variations with this, pikes, bridges, weighted walks. It really hits the trunk. He just got back from Westside with it and impressed Louie. I used it in rehabing my SI joint problems along with incline back raises and reverse hypers.,
Look for this to be the next big thing for squat and deadlift work. Not to mention just plain strengthening the trunk.