Conspiracy?

There's a lot of speculation about whether 9/11 was an "inside job." I am not convinced, but will try to keep an open mind.

I do believe that there were cover-up conspiracies behind the Kennedy assassination and the Roswell incident.

What are your thoughts - which events in our history (say, in the last 100 years or so) do you think involved conspiracies? If you have arguments and/or links, either for or against, and would like to share them, I'd love to hear about them.