I love Target's store brand hot cocoa mixes, made with soy or almond milk. I particularly like the coconut flavor and the peppermint flavor. I also like Ghiradelli's cocoa mix - double chocolate or hazelnut flavors.
It would be kind of nice to have one that is "just add water," but I haven't come across a vegan one yet. I have heated chocolate almond milk, which is good but not quite as rich as I am used to cocoa being.