Bottle Cap Keychains
To make these, you will need a very small drill bit, and a drill. Drill a hole into the top inside rim, on a safe surface. I use a scrap piece of wood. Attach a jump ring, you may need 2 of them if your attachment (Keychain) does not have one. These types of attachments can be purchased at most craft stores. These are fun to make, great gifts for kids getting their license and make nice gifts for sending "fun" mail to someone.
Bottle Cap Magnets
I have also seen jewelery, such as earrings and necklaces made from bottle caps. I just may have to make a few of those too. Although, it's getting harder to find beverages sold in glass bottles. Most beverages are now produced in plastic bottles, with plastic lids (which are very difficult to recycle). There is one place that does recycle plastic caps: Aveda Salons.