I don't know why I've never tried them before, but yesterday, I had DH pick up some Mr. Clean Magic Erasers at the store and I'm sold! With a tiny bit of scrubbing, all crayon and pencil marks came off my walls. With a bit more effort, all the scuff and shoe marks came off. The only thing that didn't come off was some of the ball-point pen. It really was magic!
So happily, my entire house is no longer a tribute to my children's artistic ability.