This is a fun research essay I have done several times with different classes. Students have to research a conspiracy theory and explain why the theory cannot be proven true. (You can choose to have them debunk the theory too but I only ask them to explain why the theory cannot be accepted as a fact.) Students learn both to research but also how to look for "holes" in arguments.
This file includes an overview of the essay requirements, a powerpoint reviewing facts, opinions, and theories; a YouTube video of the top 25 conspiracy theories; and a powerpoint reviewing the conspiracy theory that Michael Jackson is still alive (to get them started and help clarify what is expected of them in the assignment)