Ok I think I got most of the easy ones, but some of these have a certain likelihood of being incorrect. Anyway I found:
Bruce Lee (by the ship)
Ghengis Khan
Hitler
Bill Gates (??)
Charlie Chaplin
Mike Tyson
what looks kinda like a young Elvis
Queen Elizabeth
Albert Einstein
William Shakespeare
Napoleon
Fidel Castro (??)
Marlo Brando (for some reason he's in Godfather role)
Abraham Lincoln
Ghandi
Marilyn Monroe
Michael Jordan
Prince Charles
George Bush looking through a telescope??? (Far right, top row)
Yao Ming (??)
Ceasar Augustus? (Far right, top balcony by plant, wearing robe/toga)
what looks like James Cameron but most likely isn't
Martha Stewart
Bill Clinton
Audrey Hepburn (by piano in Breakfast at Tiffany's role)
James Dean (??)
Harrison Ford in Indiana Jones role?? (near middle by Bruce Lee, wearing hat, smoking a cigarette)
J.S. Bach (at the piano, obviously)
Let me know how many I got wrong and if you get any of the billion that I didn't know!
PS- What the FUCK i the thing at the middle bottom at the feet of the girl standing to Einstein's left??!!