I've noticed a few times when I've accidentally contaminated
my chocolate with some freshly ground coffee from my
coffee grinder, that it is a pleasing combination. Whymper
(in his famous book) mentions the use of coffee as a flavor
additive to chocolate. He recommends its use at levels
below which it is discernable as coffee, of course, but I
suppose the more richly burnt notes of coffee mesh well
with certain chocolate flavors which would make it a good
additive (perhaps as a substitute for over-roasting the
cacao beans -- thus giving you the best of both worlds).

I haven't tried any of the coffee-flavored, high-cacao-content
chocolates. I don't want to waste time sampling the losers.
Who makes the best ones?