Today I did the long (about 45 minutes) workout on Bob Harper's Totally Ripped Core.
Gosh, Harper just makes it very clear that the common conception of abdominal crunches being ineffective only exists because every other instructor out there is a wuss. He has you do them fast, without rest, and at a variety of angles and oh my gosh does it hurt.
Also? His plank circuits are vicious enough that you're relieved when you finally get to do stand up and do insane-jumping-around cardio stuff. Only not for long, because the insane-jumping-around cardio stuff is vicious, too.
But it's so well-designed. None of the pain is injury-inducing pain, just muscles-being-pushed-to-get-stronger pain. Love this workout.
(I might double-post this to my other blog, as a review. I'll have to check and see if I've reviewed this DVD there already.)
ETA: I did review it already! Here's a link, if you're interested: http://churchyear.blogspot.com/2012/08/exercise-dvd-review-bob-harpers-totally.html