I love the Montezuma 100% chocolate (8g carbs per 100g), though it doesn't melt in the mouth quite as gloriously as the Lindt 90% (14g carbs per 100g). The downside of the Montezuma bar is that few shop sell it, but worse, that only part of the bar is divided into squares that facilitate dividing it into low-carb-friendly portions. Nearly half the bar is not marked into squares, but instead stamped with the Montezuma logo, and the bar is too chunky to be at all easily broken. I did send Montezuma an email complaining about this, but got no real response.
The big advantage of Montezuma, beside its very low carb content, is that it is one of the very few dark chocolate bars NOT to contain de-fatted cocoa powder. I understand that the de-fatting or Dutching process lowers the polyphenol content. So if like me you like to imagine that you are helping your immune system by indulging in dark chocolate, Montezuma is the brand to go for.