In the United States, FAA regulations require that "If requested by passengers, their photographic equipment and film packages shall be inspected without exposure to an X-ray system." (source: Section 108.17(e) of FARS.)
[Note: after 9/11, some airport personnel try to tell you that this isn't true anymore. But the current TSA guidelines still allow for hand inspection. Keep a few high-speed films (>ISO 800) in your bag and tell the security personnel that you'll be going through more than five X-ray machines on your trip. This makes it difficult for them to stonewall you. If they do, ask to speak to a supervisor, and ask that supervisor to show you the current TSA regulations regarding hand checking of film.]
It helps to be polite and to facilitate easy hand searches. I always carry my film removed from film canisters (which I pack in my checked luggage) and instead in a clear bag that I present at the security checkpoint, making it as easy as possible for the security personnel to view the contents.
If you arrive with film in boxes, they will be opened. If you arrive with film in canisters, often the security personnel will open one or more to check to see if there's film in them (that's even true of the clear Fuji canisters!). If you ask them to hand inspect your camera, you will be required to show that it is an operative camera, so make sure that you've got fresh batteries in it! They may even require you to take a picture, or if film is not in the camera, to open the back. But if you don't have film in your camera, just let it go through the X-ray machine.
Outside the US, things are not as clear. I've never been able to get through security in the United Kingdom without having them X-ray all of my non high-speed film. Still, the tactic that I point out for the United States works well in much of the world, so try it.
