I am not sure if this is the case everywhere, but from what I've seen, non-dairy creamer is NOT vegan! It always seems to contain a "milk derivative" or some other animal product! Before I was aware of this (and before I totally eliminated dairy from my diet), I tried it and thought it was a great substitute for "half-and-half".
I have tried the Silk soy creamer, but unfortunately I usually find soy milk to be "chalky" and not very tasty (unless it is flavored with something -- like chocolate -- but I don't think the flavored ones are creamy enough for coffee/tea!).
I found a vegan creamer on www.veganessentials.com (it's called "Vegan Instant Creamer"), but I haven't ordered it yet...before doing so, I would love to hear from some people on the forum who have experience with this or any other vegan creamers out there.