What is the best book about ancient aliens, mysteries of ancient civilizations etc?

Chariots of the Gods.

The author, Erich Von Daniken, is very controversial and has even admitted that he lied in some parts of his books, but that doesn't matter. The idea he proposed makes perfect sense. I've done research on the Ancient Astronauts theory and have come to the same conclusion that religions and ancient cultures were influenced by alien beings, and that extraterrestrials cross-breeded with creatures of the Earth to create Man (in their own image).

Eric von Daniken is a fraud, idiot sensationalist dog ****.

Read anything by Zacharia Sitchin

Any books by Erich von Daniken will give that to you. Here's his homepage.

'Chariots of the Gods?' by Eric von Daniken'

Alternatively, watch the movie 'Stargate' and the the TV series 'Stargate SG-1' which is just as entertaining and equally as true.