Also, skeptics of the ancient aliens theory should seriously watch that video SixSenseEagle embedded. I'm not sure that I fully subscribe to the idea that aliens built the pyramids but there is a whole lot of weirdness surrounding the Egyptian pyramids. For instance, supposedly they were constructed in 10-20 years. Even with the slave labor provided by the Hebrews that seems like an incredibly short amount of time for such a massive undertaking. Even with our modern science and construction equipment that would be quite the time crunch.
And have you ever seen what the interior of the pyramid looks like? Here:
Doesn't that seem odd? Why would they build it like that? It's an inefficient use of space not to mention much harder to build. Some of those hallways are so short that you have to stoop over or even crawl to get through them, then they open up into these big(ish) chambers. I feel reasonably confident saying that there are no other structures in the world laid out like this. It doesn't look like it was designed by humans, we wouldn't put it together like this. Seriously, watch that video. Yeah I know, Ancient Aliens isn't exactly the most scholarly source but they raise a lot of good points, even if they immediately jump to the conclusion that it
must have been aliens.
My favorite out-there theory is the one put forth by engineer Christopher Dunn, that the Giza pyramid was in fact a huge power plant running on a massive chemical reaction. He wrote a whole book about it, I've been wanting to read it.