Sherlock Holmes could be an exciting crossover. Imagine the logical and observant Holmes trying to solve a mystery that involves Blackbeard's pirate activities. Blackbeard, on the other hand, would be trying to outwit Holmes and continue with his piratical ways. It would be a clash of two very different worlds - the world of piracy and the world of Victorian - era detective work.
A crossover with Gandalf from 'The Lord of the Rings' would also be fascinating. Gandalf's magic and wisdom against Blackbeard's brute force and pirate cunning. Maybe Gandalf is trying to stop Blackbeard from getting his hands on a powerful magical item that has found its way into the pirate's world. It would create a story full of epic battles and moral dilemmas.