Opening cheap locks like those found on budget lock boxes, file cabinets and desk drawers. (misspent youth)

Sticking into electrical sockets to trip breakers or blow fuses (preferably, while held in insulated pliers). (more misspent youth)

Projectile for use with a rubber band or piece of surgical hose to annoy other people or creatures (maybe even stun or kill small ones). (are we sensing a theme here?)

Lots of them linked together to make chainmail armor.

Who hasn't made a paper-clip chain? (Not useful for much.)

Scrape the dirt from under fingernails.

Put through the holes on the end of small tools to make them easier to hang on a peg board.

An emergency replacement for a blown car fuse (just be careful that whatever caused the fuse the blow doesn't wind up catching fire).

Temporarily short two circuits together on a PC board to clear computer's CMOS/password or reset many other devices.

Cross two terminals of a battery to light a fire (don't burn your fingers!)

Sharpen one end to make a crude fish hook, gaff or dart for a blow gun.

Key-ring.

Trigger for a snare.

Improvised Christmas ornament or light hangers.

And, of course, holding sheets of paper together.