My son and I enjoyed David Christian's Teaching Company lecture series called Big History and he has also now authored a college textbook by the same name. There is also a high school curriculum online, but it is more simplistic than the lectures/book.
Another text that is excellent is Robert Strayer's Ways of the World, which is also college level. I actually read the entire thing aloud and found it to be very well written.
I agree with the others that Lies My Teacher Told Me is good, but be sure he has a good background in American history first--it's important to have been exposed to the lies to be able to appreciate the book. There is a Teaching Company course called The Skeptic's Guide to American History that sounds like it might be similar, but I haven't seen it.
We have also had success with reading books on current issues such as Fast Food Nation and The Omnivore's Dilemma.
