Soy milk can be used interchangably with regular cow's milk, though it contains less fat than whole milk. It does have kind of a beany, chalky taste that can break through in baked goods with mild flavors like vanilla or lemon flavored items. But with stronger flavored items like chocolate, caramel or nut flavored pastries you would generally not know if soy milk or cow's milk was used if tasted side by side.
I've had a lot of success using those new nut milks like almond milk and hazenut milk. The flavor is great as is the texture and the price is roughly comparable to soy. Blue Diamond makes several flavors of almond milk and I believe, the other brand is Pacific or something like. They come in shelf stable packages.