I've tried a variety of dairy substitutes. Some I liked, some I didn't.
For butter, I like Earth Balance margarine. As far as I'm concerned, it tastes just as good as butter.
For milk in my cereal, I use vanilla almond milk. It's also good enough to drink straight. I also like chocolate soymilk, preferably Silk brand.
For ice cream, I like the Soy Delicious Purely Decadent Mocha Almond Fudge. I tried the coconut milk version, but it tasted too coconutty for my liking (I like coconut but in small doses) and tended to overwhelm the overall flavor of the ice cream, so I prefer to stick to the soy version.
I don't like any other dairy substitutes. I've tried the Tofutti Better than Cream Cheese, but it tasted kinda gross to me, sort of what spackle might taste like. Same thing with the Better Than Sour Cream.
By the way, I think this thread should really go in the Vegan forum, since most vegetarians such as myself are willing to consume dairy products, and vegans prefer to avoid dairy products.