My daughter has recently discovered duct tape. Not the ordinary, silver stuff, but the new and improved (for crafts that it) duct tape. We purchased several rolls from Joann's and she was ready to roll. She watched several instructional videos and made herself a bag, a belt, and several wallets. It comes in loads of different colors too, and even some prints (camo, polka dot, floral, etc.)
These are the video's she watched from Monkey See These pictures are also fun to look through.
And, here is the actual Duck Tape Brand website that will give you lots of ideas.
My son also loved playing around with it - although for a 3 (almost 4 year old) it was still a bit challenging. My daughter is 7 (almost 8) and is able to make just about anything after watching the videos.