Chocolate and coffee taste great together -- I like a roasted coffee bean covered in dark chocolate, or an extra-dark bar with the coffee chopped up in it. And of course there is mocha!
The two share more than caffeine and rich flavor, however. Coffee and cacao can grow in similar climates and can have regionally distinctive flavor like wine. Most of all, they share a similar political economy. This New York Times article focuses on Venezuela, but it is true everywhere that cacao, like coffee, is rarely as lucrative for the grower as it is for those process it for gourmet markets.
On my next coffee tour, in fact, we will include a day or two in the nascent cacao cooperatives of northern Nicaragua. There, independent farmers are just beginning to get organized and to take control of the production chain, so that they can share in the profits. Otherwise, post-colonial trading patterns persist, ensuring a wide gulf between producers and consumers.