1. Gift them out as paperweights
2. Use them as targets for a high powered rifle http://www.viddler.com/explore/HardOCP/videos/32/
3. Or, if the drives are still in good shape, use them as a backup solution. Say you have some important documents that don't get updated very often, stick one of the drives in a USB chassis, backup your data to it and drop it in a safety deposit box in a bank, or simply keep the data in separate locations in the event a disaster occurred.
While #2 might be fun, #3 does make practical use of older smaller capacity drives while providing your data some additional security.