Most techniques used for preventing rust involve coating the iron or steel item with some material which does not allow water or oxygen to get through, as both of these are needed to form rust. Common substances for coating iron and steel are: paint (there are special anti-rust paints which do not crack or peel, letting air and water in) and oil. You can also put a thin layer of a different kind of metal on top of the iron or steel, by the process of plating. Chromium is a common choice, particularly for car bumpers and decorative trim. Hence the name "chrome" for the shiny, flashy parts of cars -- it's really steel with a thin layer of chromium on top to keep it from rusting. Nickel and gold are often used too.
You can also make an alloy of the iron with other elements to form a steel which will not rust (or at least won't rust as fast). These are called "stainless" steels and are used for making knives, forks, and spoons, specialty plumbing, the backs of wristwatches, and a variety of other stuff.
To make stainless steel, just add chromium (around 20%), and nickel (5% to 20%). Smaller amounts of manganese, silicon, carbon, phosphorus and sulfur are used.
(republished on 07/13/06)