Duncan Hines produces those old standby cake mixes that so many of us have grown up with. The flavors have been specially formulated (in a lab no less!) to perfectly greet our taste buds, and the leavening is added in just the perfect amounts to create a nearly foolproof cake.
I confess, that Duncan Hines no longer makes its way into my shopping cart, as I have over the years banished hydrogenated oils and high fructose corn syrup from my family's diet. Nonetheless, when frugality is in order, these cake mixes can be found on discount for a good price. Plus, they recently went back to their Kosher parve OU status. They still may contain traces of milk due to manufacturing processes, but the OU-parve stamp is pretty good for general milk-free purposes.
To the best of my knowledge, most, if not all, of the Duncan Cake Mixes are OU parve (including the yellow, marble, and devil's food mixes), and thus dairy-free, so you should have quite a few flavors to choose from! But as with all food, check the ingredient label to be sure!