I've got some old, torn-up jeans that I don't know what to do with (short of throwing them away), so it's quite nice to find this post at Life Hackery of 25 ways to recycle your old denim jeans.
I like this one the most: 14. Make a unique denim bulletin board, though I doubt I'm crafty enough to make it!
Here's the Link - see if you can add any more ideas to the pile - Thanks Kurt!
I've also made and apron, cusions and a footstool/square beanbag thing.
One metalworker I knew used a cut-off leg as a workshop cap.