Sorry! I meant to add the title after I had gone upstairs and gotten the book, so, of course, it left my mind the minute I left the computer!
The main book I will be using is A History of the United States. Amazon has it used for as low as $6.50.
That being said, I also have a book which is very similar, but was written for a younger audience. Tracy, I don't know how old Samuel is, but I believe this might be even better for him. This is Our Country Begins. Amazon has it for $5. This book has even more activity suggestions, so while the text is too simple for my older kids, I will mine this one for activities.
Before I found these books, I had planned to use The Story of America, a National Geographic Picture Atlas, which Amazon has as low as $1.50. My copy is from 1992. This one is just beautifully laid out with plentiful beautiful pictures. I will still draw a great deal from this one for the pictures and maps. There are many many pictures and only a few maps, so I'm not sure why they call it an atlas. Still, it's a lovely book!
By the way, I couldn't deal with all the pictureless posts, so I retrofitted them with random US History photos. I particularly like the black and white one: its a historical reenactment of the sewing of the first flag, staged in 1915!