I brewed a chocolate beer last year. I'll try to get the recipe posted tomorrow, but it was based on a recipe in Papazian's second "Joy of Homebrewing" book. I used dark chocolate from a variety of sources. Most of it was left over Valentines day chocolate, like Dove brand. I used about a pound of chocolate, and added it at the very end of the boil.
When you are transfering the beer from one fermenter to the other, you want to be sure not to siphon anything from the surface of the beer. The cocoa butter in the chocolate forms an oil slick of sorts, and that can be a real head killer. I actually added an extra siphoning step on bottling day, just to get any remaining oils out of the beer.
It turned out great. There's plenty of chocolate flavor, and a nice brown creamy head. I recall that the recipe went something like this:
5 lbs 2 row malt
3 lbs light DME
1/3 lb Chocolate Malt
1/3 lb Roasted Barley
1/3 lb Black Patent Malt
1 lb Wheat
1 lb Munich or Crystal malt, (I can't remember)
10 oz Dark Chocolate (I upped it to 1 lb)
I don't remember the hopping schedule, or type of hops, but it was pretty light on the hops.
I'll find out more and post it later.