The Egyptians. Such ingenuity as technological advancement at a time when every other civilisation was basically banging rocks together.
The Roman Empire, for obvious reasons.
The Crusades, very interesting era in my opinion, I'd love to see people fight with such religious fervour.
The Renaissance, The excitement of the discovery of the new world, and to be a colonist to such a strange land would be great.
WWII, to see people gathering together for one cause.
after that various places in the future, first landing on Mars, first colonisation of another planet, solar system, and to see Humanity develop into a Type I, II and III civilisation. (IF any of this ever happens, which I sure hope it does).
Dream Theater - "Sabre120 and Jongleur officially win. That is all."