What are some argumentative essay topics?

I will answer your question, but first I would like to add a caveat from my perspective as an English Composition and Rhetoric instructor for first-year students at a large university: the best topic for an essay—regardless of the "genre" of that essay—is one that you are passionate about. If you locate a topic for an essay online with little regard to how you feel about that topic, you will likely struggle with the writing process. This is especially true for argumentative essays, which require you to take a strong stance and command evidence in your favor to convince your audience of something. 
Now that that has been said, let me share with you some of the argumentative essay topics that I have especially liked from previous students:
Humans are natural and historical explorers, and the benefits of renewed efforts toward space exploration transcend monetary and market value.
The path of addiction is not made by choice, and even when regarded as a social transgression, there is still no merit for the kind of compassionless legal punishment that is reflected in our current drug laws.
Our debate around the depiction of violence in film and how it should be regulated needs to shift to a focus on how to educate moviegoers to make informed decision about the materials they consume.
I would advise thinking deeply about what you really, truly care about and constructing an argument around that!