Giselle Weybrecht has sought out the world's best hot chocolate at 450 venues in 55 countries. You can read about her quest here.
This is the base recipe I use every day. A good hot chocolate starts with good chocolate. I prefer 72% but you can go darker or even use milk or white chocolate. My favourite is Guittard, from a family-owned company in the US, which I can't get here. In Australia I've been using Callebaut and Valrhona, but would rather find something local.
In terms of ready-made powders I'm a fan of Grounded Pleasures from Ballarat. Mork makes a nice dark cocoa, and Monsieur Truffe in Melbourne does a little hot chocolate kit with chocolate chips. I also melt down bars from Bahen and Co (a WA bean-to-bar company) but that makes for expensive hot chocolate.
I also add herbs and spices. A handful of fresh mint leaves, cardamom, grated ginger or even thyme are some of my favourites. For even more flavour, steep the herbs or spices in the milk in the fridge overnight. I use about a teaspoon of dried spice, or a small handful of fresh herbs.
I like to add a tablespoon of cocoa to this recipe below to make the drink creamier. If you're using a really good chocolate, though, just let the chocolate shine on its own.