I don't believe in man made global warming. I think the Earth is a lot more resiliant than the green movement paints it and the green movement is more anti-capitalist then truly concerned with saving the planet.
I don't think there is intelligent life away from Earth. There are tons of factors besides a planet having a star to provide energy. You have to have the perfect sized planet, the perfect distance from a star, the right atmosphere. We are learning so much more about space, but we aren't any closer to finding little green men then we were in the 60's.
I believe in a few of them. The JFK/RFK assassinations were done by multiple shooters. There is too many weird things going on that allowed it to happen. I believe in coincidences, but Ruby shooting Oswald while all of Dallas PD looked on, screamed "Cover-up". RFK's assassination, I can either way on, but after JFK, you would think the Secret Service would do a better job of putting bodies in front of this guy. The fact that Sir Hahn Sir Hahn admits to a conspiracy inches it closer in my book. Yet, the guy could be a raving lunatic that is why that out of the two, I can see it being a lone gunmen.
Aliens, I believe. Too many documented photos, videos and stories just to toss it away. Now, what they want with Earth and if the government is involved, I have no clue. If they do exist I doubt the government knows their true agenda unless, its something as simple as Earth has nice beaches and we get off on anal probes. We are also finding new Earth like planets almost every six months now, so its not impossible as others make it sound.
Illuminati. Tough call. Since there was a group or groups like it in the past, doesn't mean they are not around now in some form. Yet, the groups in the past were not all powerful and unified. Many splinter groups emerged from the original thus we have a lot of theories on the Illuminati that are mixed in with others like the Masons. I think the closest you can get is maybe a few corporations and governments working as gatekeepers in a chaotic world, but they are not as power as we or they think they are. It will be next to impossible to improve if they were real since they would just deny it or scream National Security. I am sure there is a group too calling themselves the Illuminati out there, but they have little or no power. Also, Allan Moore went crazy after From Hell, how else do you explain the new League books.