The Cartoon History of The Universe Volumes 1 & 2 by Larry Gonick.
My personal favorite is early Chinese history, since it's fairly unfamiliar territory and Gonick seems to have been very taken with it to and here he pauses to really illustrate the personalities. The emergence of the Chin empire deserves it's own I, Claudius equivalent (which I'm sure it has, I just don't know about it.) I will never forget learning about Lu Pu-Wei, Hsiang Yu's epic rivalry with Liu Pang, Li Ssu's brilliant and eloquent defense of tyranny and evil in a ruler centuries ahead of Machiavelli.
I will concede Gonick does not have the most sophisticated sense of humor (ugh, puns are reprehensible things) and sometimes it might seem intrusive. Still, recommended reading even if you usually hate comics.