Soy milk has long been a popular alternative for people who are unable to drink cow's milk (usually due to lactose intolerance). But rather than drink soy milk because you have to, more and more people are deliberately choosing soy milk because of the added health benefits.
The benefits from soy are still being disputed, though it is generally accepted that soy milk contains a high number of very healthy compounds. Soy milk is high in protein, and because it is made from beans, also contains considerably more fiber than cow's milk.
Speaking of being made from beans, how exactly is soy "milk" made? Beans are cleaned and soaked overnight, and then pureed. The solids (called okara) are strained out, and the resulting liquid is boiled for about 10 minutes. A little simplified, but that's the basic idea. Of course, soy milk is also sold in most major supermarkets these days. There are also a number of kitchen gadgets on the market for making home-made soy milk (some links at right).
Back to the healthy aspects of soy milk. Besides the extra protein and fiber, the biggest benefit in soy milk are the isoflavones. Sounds complex, but basically isoflavones are actually chemicals very similar to the hormone estrogen. Isoflavones are connected to a whole host of health issues, with the most prevant being the prevention of many cancers, heart disease, osteoporosis and more. Berkeley Wellness Letter has an excellent article on soy isoflavones that can explain more.
Soy milk isn't fat-free, though some people think it is (I suppose because its made from beans). Soy milk does have a bit more fat than 2% cow's milk, but none of the nasty cholesterol (of which there is approximately 20mg per cup, in 2% cow's milk).
The largest downfall of soy milk is the lack of calcium. Soy milk has only about a quarter of the calcium, compared to cow's milk. Many soy milk manufacturers are adding calcium to their products, but studies show that it is not as healthful as naturally-occuring calcium. Thankfully, calcium is easily obtainable from other sources such as sardines, almonds, many beans, and several varieties of green leafy vegetables (like kale and collard greens). Of course, if you are able to handle dairy products, you can get your calcium from yogurt and cheese.
I suppose when it comes to adding soy milk to one's coffee or tea, it might seem like a moot point considering the quantity. But when it comes to your health, you should make every drop count.