I'd have to join in and say a small(er) amount of a good, dark chocolate is the way to go, as there's no substitute for chocolate, really. The darker it is, the less you'll eat, likely. It's the cheapest milk chocolate candies I can swallow with abandon.
But if it's a replacement for cooking, not eating straight (and this wasn't your question), then the answer is carob, and see also:
If you want a nutritious chocolate 'fix' *and* can control yourself, you could do worse than Silk's chocolate soy milk ... smooth, rich, nutritious. It's a nice treat.