It seems that everyone has a different way of cooking plain rice. Here are a few of the approaches I've seen; if you've got one that's not here already, then please let me know so I can add it.
Just boil it
Ben suggests: bring a large pan of water to a rolling boil. Add the rice and stir. After 11 minutes (or once the rice is cooked), drain the rice using a colander and serve.
Boil and steam
Roz's approach: bring a large pan of water to a rolling boil. Add the rice and stir. After seven minutes, drain the water off using the pan lid. Leave for another seven minutes with the lid on, then serve.
Alexis Soyer's approach, from Soyer's Culinary Campaign (1857, p515):
Put 2 quarts [2.2l] of water in a stewpan, with a teaspoonful of salt; when boiling, add to it ½lb [225g] of rice, well washed; boil for ten minutes, or till each grain becomes rather soft; drain it into a colander, slightly grease the pot with butter, and put the rice back into it; let it swell slowly for about twenty minutes near the fire, or in a slow oven; each grain will then swell up, and be well separated; it is then ready for use.
Boil, rinse and steam
The White House Cookbook, by Mrs F. L. Gillette and Hugo Ziemann, dates from 1887. These instructions are from the recipe for mullagatawny soup.
A dish of rice, to be served separately with this soup, must be thus prepared: put three pints of water in a saucepan and one tablespoonful of salt; let this boil. Wash well, in three waters, half a pound of rice; strain it, and put it into the boiling water in saucepan. After it has come to the boil — which it will do in about two minutes — let it boil twenty minutes; strain it through a colander, and pour over it two quarts of cold water. This will separate the grains of rice. Put it back in the saucepan, and place it near the fire until hot enough to send to the table. This is also the proper way to boil rice for curries. If these directions are strictly carried out every grain of the rice will separate, and be thoroughly cooked.
Moof gives a Spanish recipe: Rinse the rice in water in a bowl to remove the loose starch. Place in pan with one and a half times its volume in cold water, put the lid on, and cook until all the water's evaporated.
Rules of Thumb describes
way to work out how much water you need:
To cook rice, rest the tip of your index finger on top of the rice
and add enough water to reach the first joint.
This works for any size pot.
Absorb and steam
Joseph Lorenzo Hall's approach: bring 1.5 times the volume of rice in water to the boil, then turn the heat down to a simmer; cook the rice in it for 15 minutes, then cover (without draining) for a further 15 minutes to steam.
EKR approves this approach, suggesting that it can be varied by adding pulses or coconut milk.
This is the same approach that cheap rice cookers use. From the instructions for my rice cooker: add one cup of rice and one and a half cups of water per person to the rice cooker, stir, put the lid on, and turn the rice cooker on. When the light goes off (by which point all the water will have been absorbed), wait for fifteen minutes, then serve.
Fry and absorb
Frying rice with spices and other ingredients, then cooking it with water or stock until it has been absorbed is the basis of various rice-based recipes: for example, Mohammed Aslam's Kashmiri pilaff, Elise's Spanish Rice, and casseroles like arroz con pollo. This definitely isn't plain rice any more, though...
Soak, fry and boil
Martin Williams wrote in with his recipe:
While I have tried several ways of cooking the simplest of foods, the method that works for me is to soak the rice for at least 30 mins and drain washing through a colander several times, cover the bottom of a pan with oil with salt to taste depending on how many are being served, coat the rice in oil on a low heat then add boiling water twice that of the rice, bring to the boil and simmer for 10 minutes, drain rice through a colander, then use a kettle of boiling water to remove excess starch. Drain for a few minutes... perfect rice.
Boil and bake
Danno describes the New Orleans approach in his Creole Boiled Rice recipe — he boils the rice for 11 minutes with bay leaves, then bakes it with some butter for 15 minutes.