Anyone who has spent any time in Asia will know that a rice cooker is an indispensible appliance there, and if you like rice at all it can be one for you too. In the poorest most rustic households the rice cooker will be a simple aluminum or clay pot placed over a charcoal fire, but most houses and restaurants with electricity have an electric rice cooker - capacity perhaps 6 or 8 cups for a small household, up to 50 cups or more for a busy dining room. Many restaurants also use rice steamers, but I have no experience with them and so cannot speak about them. Electric rice cookers I know well, though.
Most consist of an outer metal or plastic-clad sleeve with feet, a heating element and a thermostat inside at the bottom, an inner sleeve which fits inside the outer sleeve resting on the heating element, a plug, and a switch which almost invariably has two settings: "rice cooking" and "keep warm". (These days the inner sleeves are usually non-stick, and if you're still using one with an aluminum sleeve to which your rice sticks, throw it away and buy a new one. These new ones are way easier to clean, and besides, aluminum cookware has been associated with Alzheimer's disease, and we don't want that now, do we?) In addition, your rice cooker will probably come with a small plastic measuring "cup" and a plastic paddle which is used to remove a serving of rice with a graceful scraping motion. It's plastic so it won't scratch the inner sleeve.
I put "cup" in quotation marks there for a reason. The cup is not actually a cup, it's about 3/4 of a cup (180 ml). According to the manufacturer's directions, you measure out your rice using the "cup" measure, then add water to the corresponding "cup" measurement conveniently located on the side of the inner sleeve. But proper proportion of water to rice is key to successful rice-making, and the amount of water you add depends on the type of rice you're using, not on the markings on the side of the sleeve. For jasmine rice, the kind I make most often, 1 cup (real cup: 240 ml) of rice to 1-1/4 cups (300 ml) water; this works for basmati rice as well. For brown rice, 1 part rice to 2 parts water; for wild rice, 1 part rice to 3 parts water. I get rid of that deceptive plastic not-cup and measure my rice and water with a real measuring cup. But that's just me.
Okay, the rice is poured into the inner sleeve and then (usually) rinsed a few times. Wipe excess water off the outside of the inner sleeve so you don't short out the heating element. Add the appropriate amount of water to the rice (see above for proportions), put the inner sleeve in its spot in the outer sleeve, place the lid on the thing, plug it in, turn it to "rice cooking", and voila! Perfect rice will soon be yours.
I teach Thai cooking, and I have often waxed poetic about the mysterious ability of the rice cooker to know when the rice is cooked and flip itself to "keep warm". It knows, no matter what kind of rice it is or how many cups you put in there. Actually, a little research steals one of my good lines and reveals that the principal is quite simple. What the rice cooker does is bring the water to the boil (212°F at sea level for the detail oriented) and then maintain the pot at a steady temperature. When the water is thoroughly absorbed by the rice, the temperature in the inner sleeve abruptly rises, at which point the thermostat recognizes that the temperature is too high, automatically setting the heating element to its lower setting (140°F), where it will happily maintain itself for hours. Ingenious, no? (The same principle is at work in the automatic drip coffee maker and the automatic egg hard boiler, apparently. Automatic egg hard boiler?!? Now that's obscure. But I digress...)
There are a few more things to know about rice cookers. The cheapest kind have simple glass lids that just sit on top of the inner sleeve, while the slightly more expensive ones have lids that seal and are released by pushing a button on the handle. These latter are better because they keep more of the fluffy steam in the pot while the rice is cooking, and are much better at keeping rice warm for long periods of time. The rice in the cheaper cookers can get kind of crunchy and dry after an hour or so. The most expensive rice cookers, like the Zojirushi one, have microcomputerized neuro fuzzy logic temperature control systems. Wow. They have settings for white and brown rice, "mixed" rice, sticky rice, and congee, as well as texture controls: regular, softer, or harder. This fancy rice cooker has a "new spherical heating system-surround heating system" which "ensures perfect rice cooking every time". Double wow. I want one of those, but they're pretty expensive. I've settled for the mid-range one with the sealing lid. If you guys want to chip in next christmas and get me one of those fuzzy logic ones, I'd be thrilled, though. Promise.
I should also mention that I know enterprising Asian students who can prepare entire delicious multi-course meals using only a rice cooker. There's even a cookbook filled with recipes devised specifically for rice cooker cooking: The Ultimate Rice Cooker Cookbook by Beth Hensperger and Julie Kaufman.
Bottom line on rice cookers: not essential, but damned convenient. Perfect rice every time, minimum hassle. If you want one, shop in Chinatown if at all possible; they'll have the best selection.
Thanks to "How Stuff Works" (www.howstuffworks.com) for finally revealing the ancient and mysterious secret of the rice cooker. And see also How to cook rice and Ack! My rice is ruined! Or is it?