Okay, there's soy milk and rice milk or water for substituting cow's milk in recipes. But what else? Juice can be used(you may wish to cut down on the sugar called for elsewhere in the recipe). If you use an acidic juice(orange) you may need to replace some of the baking powder called for with baking soda(which is alkaline) to offset the acidic juice. The base and acid then bubble together to help the goods to rise. My sister says rule of thumb, if you use baking soda instead of baking powder, you use 1/3 the amount. I made muffins the other day with orange juice instead of milk. The recipe called for 2 tsp baking powder. I wanted to keep some of the baking powder, and then use some baking soda to off-set the acid in the orange juice. I used 1/2 tsp baking powder and 1/2 teaspoon baking soda.
Have you heard of zucchini milk? Zucchini can be boiled then blended up, then added to baked goods in place of dairy milk. It freezes well for use year-round! See http://www.recipelink.com/mf/31/39634 for instructions.
Nuts can be made into milk. You blend nuts and water together. You can find the amounts of nuts to water to use on the internet. My allergist recommended that my daughter and I (as I breastfeed) avoid all treenuts, as my daughter tested positive for peanuts. But sunflower seeds are not tree nuts, at least I assume since they don't grow on trees! Sunflower seed milk is even in my recipe book for my VitaMix. I'm sure it could be made in a blender.
Margarine in recipes can usually be substituted with vegetable oil or shortening, as far as I understand. I've been using vegetable oil in all the recipes I make that call for margarine or butter. Sometimes I use non-dairy margarine spread, if I think it will matter to have the butter-like flavor. Usually I don't use it because it's more expensive than vegetable oil. Applesauce also can be used instead or margarine or vegetable oil.
If you're a breastfeeding mother who is going off dairy and eggs, and you like dairy based or egg-containing salad dressings, it may help to consider hummus. I home cook dry garbanzos and make hummus in a blender. It freezes in small containers and thaws nicely. I use it on pitas, wraps, and for vegetable dip. I've also seen many recipes for salad dressings that are oil based and don't contain dairy or egg.
What dairy substitutes have you enjoyed?