Last week while at my camper in the freezing weather I ran into a little problem. The extreme cold caused many of my locks on the camper to freeze. The compartments of the camper have those key ways with the little sliding opening to keep dirt out. Unfortunately it didn't keep the moisture out. I thought I was prepared because I regularly would spray silicone into them as recommended by the manufacturer.
I finally got them open by spraying some starting fluid (ether) into them.
Right after I purchased some lock de-icer which now resides in my car.

I run into this SO often it's not funny (I deal with frozen locks all the time).

www.northerntool.com/webapp/wcs/stores/servlet/product_6970_137385_137385

A bic lighter is usually all you'll need.

I have had the same problem with the locks on my vehicle in the past.  I hold the key with my leatherman and heat it up and place it in the lock allowing the heat to sink into the lock. A couple of times and it has freed it to open.

A shot of WD40 into the locks pre season works wonders too.

i agree with tommy, hit it with WD-40 every time your there. it drives out the water. no water, no freezing.

Quoted: A bic lighter is usually all you'll need.

And if you fill that lock with starting fluid first the bic lighter will be far more effective.

If you don't have any tools or fluids you can form a cup around the lock with your hands and then blow into your hands.  While you are doing that put the key in your mouth.  This is only a temporary solution becuase your breath will add moisture to the lock as will putting the key in your mouth but it will at least get you to the store to buy something better.

WD-40 or RemOil works great for PM.  Heating the key with the lighter works well to when they are already frozen.  

As far as gate padlocks the same applies..... although I have found some so iced up I applied WD-40 liberaly and then applied the lighter.  Crude but effective.

Lock de-icer in your glove box is not to handy when you are on the outside looking in!  Use it ont he car once in a while before major temp changes and rain changing to ice and snow storms.

While you're doing PM on the locks, don't forget to wipe down the door seals with silicone, to help keep them from freezing shut.

Quoted: While you're doing PM on the locks, don't forget to wipe down the door seals with silicone, to help keep them from freezing shut.

A big +1 on that one.  Especially with the new aerodynamic door frames without the rain gutter above.