There are chocolatiers everywhere in Belgium, but the ones most worth your time and money take themselves seriously. A cool climate means chocolate makers don't have to worry about their products melting, so chocolate here, fortunately, comes without the waxy texture found in the United States. Instead, in Belgium, it's downright fluffy, especially in cakes -- often decorated with intricately carved toppings -- and truffles or pralines with rich fillings.
The grande dame of Belgian chocolate is Neuhaus, which has been pleasing aficionados for 146 years. These guys are serious; just walk into their store, in one of Brussels' trendiest shopping districts, and you will find a marble-walled, chandeliered boutique where the sales clerks wear black suits. Neuhaus' dark chocolate (they scoff at chocolatiers who use additives instead of pure cocoa) is serious stuff.
For a different and less snobbish taste, try Leonidas, where folks line up outside the shop's large open front windows to tell the white-clad, hair-netted women inside what they want. Think Seinfeld's "Soup Nazi," except that Leonidas employs terrifying lunch-lady types: You'd better know what you want or get out of the way, and lingering could cause a riot among the impatient blue-collar workers waiting behind you. If you're not sure what you want, throw yourself at the ladies' mercy and they'll put together a mix.