I am looking for different lower back exercises. I have a weakened back (due to a back injury from the gym along with a bone defect) and I really need to strengthen it to help with lower back pain.

I have flipped through magazines, etc, searching, but low back exercises seem to be hard to find... I do cobras, planks and bridges, but I am looking for a few others to vary my routine. I am looking for some that do not bear much additional weight, since my back is still recovering (and my bank account from medical bills).

If anyone can help, or send me a link to a site with exercises, it would be much appreciated!