Lower back work

I feel like this is part of a core workout that is often overlooked.
At my school's Abs & Low Back core aerobics class they offered a few exercises- mostly lying on our stomachs and raising our torso and pulsing up and to the sides. About 90% of the class was ab work, though.
Anyone have any other good motions for working these muscles? I think the benefits are great, especially for swimming, but I can only do so many of the same thing...