Back in September, I did a post on the subject. After thinking about it, from the two crossover idea I gave, one might be more interesting than the other.
Black Butler cross with Count Cain.
Both storyline are set during the same era, both count have a tragic past and the two story are related to the supernatural world. As I said in my previous post, I could see the Queen Victoria asking Ciel to investigate the Delilah Group.