We use Belaromas drinking chocolate at work and also at home. Its good for drinking and sprinkling on the top of coffee.
The other week at ICTF I tried a new product which is apparently a powder but it looked like melted chocolate with some milk thrown in! It was nice but I didnt like the way it formed a skin on the surface so quickly. Youd have to keep stirring it when drinking.
But you probably want something more like the Belaroma product. They are the only ones I know of. I dont know if any of the site sponsers here also do drinking chocolate.