There is a lot evidence that NASA sent humans to the moon, but here are a few of the legitimate reasons to doubt
1. The missions were political not scientific.
Scientists were not interested in sending living creatures to other planets. It was very expensive and difficult with little scientific benefit. They preferred, and still prefer, sending machines. Sending humans was a political stunt, dreamed up by politicians. It was done for image purposes. From a political point of view it wouldnt matter whether the mission was genuinely accomplished or faked as long as it was convincing.
Today (2010), putting NASAs space robot R2 on the moon can be done with half a billion dollars, which is pocket change compared to the price tag of a manned mission to the moon: $150 billion.
2. Austronauts and scientists have said we dont have the technology to go to the moon today.
At least one Apollo astronaut and at least one university scientist have stated in interviews that we dont have the technology to go back to the moon today, even if we wanted too.
3. The Soviets were 1st to everything else in space, yet never sent anyone to the moon
The Russians were clearly way ahead of the US in space technology and have never sent anyone to the moon, neither has anyone else. The Soviets had already landed the probe Luna 2 on the surface of the moon in 1959 and had an orbiting satellite in 1966
4. Astronauts in the Post Apollo 11 press conference looked very nervous.
They also claimed they didnt see any stars when on the moon
5. NASAs occult, Nazi and masonic links
NASA was founded by a collection of Nazis, masons and occultists. 11 is an important number in masonry, 13 is an unlucky number. Some astronauts are masons, they took a masonic flag with them to the moon as well as a US flag. HG Wells wrote in "Things to Come" in 1933, that after the next world war, men would be sent to the moon.
6. Astronauts have claimed in radio interviews that they cant remember what it felt like to walk on the moon
7. Buzz Aldrin says he saw a UFO on the way to the moon
8. Buzz Aldrin admits the American flag on the moon is lying flat on the ground. He claims this is because they knocked it over when they left the moon
9. Why was NASAs Constellation programme such a failure
10. Moon dust has "run out" and a stimulant has to be used
Also: Fake Dutch moon rock http://news.bbc.co.uk/1/hi/8226075.stm
11. What's keeping us from Mars?
Cosmic rays are so dangerous and so poorly understood that people are unlikely to get to Mars or even back to the moon until better ways are found to protect astronauts, experts said on Monday. http://www.reuters.com/article/2008/03/31/us-space-radiation-idUSN3139657820080331