Hmmm, only because I think you are asking someone to do your homework...
1. They make great picture frames especially the old 14 inch platters.
2. They make horrible frisbees and dinner plates (juices all run out of the hole in the middle).
3. They make great shuriken when properly cut and filed.
4. They make great mirrors.
5. They make at best weird hanging ornaments.
6. If you want a reason for using hard disks in a computer, try doing a search. It has been answered on blurtit in the past.