The Short Story: Chocolate originated in what is now Mexico more than two thousand years ago and up until the 19th Century was consumed as a liquid rather than a solid. Most of us Americans have grown up on Hershey's, which is based on a formula developed about 100 years ago to allow chocolate to keep for months at room temperature. It has a sour milk taste that apparently takes some getting used to if you don't grow up with it. Nowadays I find that my tongue gets a burning sensation when I eat it. The main thing to know: what we like about Hershey's is the sugar, not the cocoa, which is--I think--less than 10% of the bar. This means that what we normally think of as chocolate is really chocolate-flavored candy. Further reading on Hershey: Emperors of Chocolate (Brenner). Further reading on the history of Chocolate: The True History of Chocolate (Coe & Coe) (the title is a play on Cortès' henchman's history of the conquests).
Good chocolate is about 10 years behind fine coffee in the United States and paying more than a dollar for a chocolate bar takes some getting used to. Why is it so expensive? Each stage of chocolate production, from growing the beans, to drying the beans, to conching, to tempering provides an opportunity mess up the final product. Thus, the best chocolate makers have to control each stage of the process to get it right. This means spending money and imposing control with a level of perfectionism that most of us won't appreciate in the final product until we've tried many different bars. Also, unlike wine, chocolate deteriorates with age, so it's best to eat it within a month rather than building a collection. The really fine truffles need to be eaten within two weeks, apparently. Further Reading: Chocolate : A Bittersweet Saga of Dark and Light (Rosenblum), The Chocolate Connoisseur (Doutre-Roussel)
Start with 70% cocoa bars without infusions of other flavors, since
almost every maker has a version of this basic model. If any one
country seems to be consistently good it is Italy, followed by
France. Amedi is quite nice and widely available. Ultimately, pick
what you like the most and don't worry about the label or the price.
My favorite at the moment is Maglio's Santo Domingo (named after where the beans were grown) bar that costs $8 for 120g at CoccoBella but if you don't want to pay a lot but still get something good, Trader Joe's in San Francisco has Valrhona's basic bar. Based on what I've read,
Godiva is all marketing and they don't put any effort into the
chocolate so I would avoid them.