For a few years I questioned if Apollo 11 landed on the moon. Clearly someone did since there are mirrors on the surface of the moon, but I figured it could have been later missions that put them there. What had me questioning the landing was footage showing that the Apollo 11 astronauts very clearly cut a circle out of a piece of cardboard and put it up to the window. This created the illusion that they were much further away from Earth than they really were. In the footage, they claim that they have the lens put up against the window, yet you see a shoulder pop into frame and hear someone say, "Get out of the shot, Buzz." I don't know why they would have done this, but these days I do 99.9% believe Apollo 11 did land on the moon. This is because of they simply didn't have the technology to fake the video footage. The linchpin of the conspiracy theory is that the footage is slowed down. That would require magnetic disc recorders far larger than what was available at the time. The biggest ones that were commercially available (they were used for sports replays) could hold about 9 or 10 seconds of slow-mo footage. The first EVA was 143 minutes! There's just no way. Even if you say "OK, well what if they used film?" There's no film grain, scratches, marks, or splices on the 143 minutes. This would require a single film magazine as big as a car tire. No way.
I'd also say that PRISM and NSA spying counts as a true conspiracy theory. People have been asserting that the government has been spying on its citizens for decades. Now it's clearly true.
Silly, but probably plausible to some folks. 
