Brodie's and probably others have used cocoa nibs. I've no idea what they are but assume they are less sweet than chocolate.
Purple Moose do a Chocolate Mousse beer which the first time I tried it was horrendously sweet, a Death By Chocolate type of drink. When I tried it last month it was a lot better and Vanilla had been included.
Call me old school, but I like to find flavours and aromas derived from malt,hops , yeast and water,rather than bits and bobs of other stuff.
"At that moment I would have given a kingdom, not for champagne or hock and soda, or hot coffee but for a glass of beer" Marquess Curzon of Kedlestone, Viceroy of India.