How does one go about liquifying things that usually lie around gaseously, such as nitrogen, oxygen, propane, etc. I’ve got my freezer cranked way down (up?) but nothing drips out when I open the door; should I get it repaired?
You often have to adjust the pressure as well. IIRC, carbon dioxide cannot become a liquid at less than 5 atmospheres.
See this article on the commercial production of oxygen. Scroll down to the commercial production section. It describes the production of liquid air which is then fractionally distilled to produce the oxygen.
Good question. Normally, they do it with compression. They take a whole bunch of nitrogen, oxygen, or whatever and compress it until it liquifies. Thermodynamics dictates that the temperatue of the gas will rise as it is compressed. This is called adiabatic heating. Instead of letting the heat build up in the gas/liquid, they draw it off as they compress it. By the time they’re done, enough heat has been removed that the liquid is more-or-less stable. They have to keep it in an insulated container, though, because it will try to evaporate again. That’s why liquified gasses are so cold; they’ll take heat wherever they can get it to become vaporous again.
According to the Combined Gas Law you don’t have a lot of options.
To get them liquid at 1 atmosphere of pressure, you need a more powerful freezer than a home unit. As stated elsewhere, pressure is the easiest way to liquify said substances.
Don’t listen to them. I’ll repair it for you. I charge $500/hr. 
For some fun, try pouring a cup of liquid nitrogen (LN2) into a small room temperature pan. Swirl the liquid until it spins in the pan. Set the pan down and come back minutes later. The liquid will still be swirling rapidly.
This is a liquid phase example that I discovered of the famous, frictionless “Dry Ice Hockey Puck” physics demonstration.
LN2 is good for freezing alcohol too.
Zenster, have you ever done a frozen tequila shot?
Diceman is correct for the gases you named. The property people take advantage of when they are trying to liquify gases is called the Joules-Thompson effect. The Joules-Thompson coefficient is the derivative of temperature with respect to pressure while holding enthalpy constant. Gases with a positive Joules-Thompson coefficient will rise in temperature when compressed and fall in temperature when expanded. To use this effect to liquify a gas it is commpressed, allowed to cool in its compressed state then allowed to expand. This is repeated until the gas is at it’s boiling point.
The Joules-Thompson coefficient is not a constant, however. It is a function of temperature. Some gases can only be cooled so far using Joules-Thompson cooling. Helium is one of these gases. Below a certain temperature, well above it’s boiling point, it will no longer heat up when compressed. More complicated methods are needed to liquify helium. One involves using magnetic fields, but I forget the specifics of it. Maybe some thermodynamicist will come along and explain it.