Ok, given the strong response to the safety pin thread I’ll start one for Alternate Uses for a Paper Clip.

1) Used to eject CD or DVD from system that is powered down
2) Heated to red hot burn through smashed finger nail to relieve pressure
3) ?

Cheers,
W-W

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.

Bending into a safety pin!

best i can do off hand is a zipper pull replacement or maybe a cut off bit to replace a lost glasses hinge screw.i don't know how to do it but i'll bet someone could come up with a way to use one as part of a "hair trigger" for a dead fall or other type of trap.

Use along with a metal twist-tie to splice together a broken heating element in an oven broiler. Like splinting a leg, use the paperclip to bridge the gap, secure on both sides by wraps of twist tie. (One of my rare McGyver moments at a rental cabin.)

The lowely paper clip can be bent to hold things together that are glowing hot.

Substitute for proper safety wire or cotter pin to keep things from falling or vibrating apart.

Really poor, but sometimes functional substitute for a hinge pin.

Can be used as a scribe to mark wood, metal, or plastic parts.

Sometimes can be used to unclog small tubing or jets.

Handy with a cotton patch to clean the little spaces of some firearms.

I keep some jumbo size (about 2" long) paperclips in many of my tool kits.

cotter pin?

Tweezers. (Some applications posted above come pretty close)

Keeping small and flat glue projects in place while the glue dries. (Obviously, this is pretty close to the original paper clip usage).

Unlock handcuffs.

Trade into a house (the story of One Red Paperclip)

WWII symbol of resistance.
Paper clip on wikipedia

The not quite true Norwegian national myth of the paper clip has been used actively as a symbol of Norwegian ingenuity. (The Norwegian inventor Johan Vaaler got a patent in 1901 for a simpler paper clip that was not quite as good as the modern paper clip. Don't let facts stand in the way of using a good myth...).

Keyboard keycap puller. So you can vacuum or dump the cookie crumbs out of your keyboard. (Or mess with your nemesis at work)

Bend it into an "omega" with the legs turned inward instead of outward.

I own a pistol (Kimber Pro Carry II) that's very difficult to field strip if you don't have the included take-down tool...or a paperclip.

I find this interesting as I have seen others ridiculed for including a paper clip in their mini kits. Obviously the ones doing the ridiculing didn't think it through and I am afraid the ones who were being ridiculed took the advice to heart and eliminated this obviously useful implement from their kit. The only disadvantage is some of the mods require other tools you may not have on your person. Still, if you might need a short length of wire for something it seems worth throwing one or two into your kit.

Also you can use one to unclog a glue applicator tip.

I can't think of anything else original to add that hasn't already been mentioned so ... yeah ... what everybody else said.