I hate a history that is merely dates, places, battles, and names. I want to know about the people who made things happen, the people who stand in the shadows...
Just off the top of my head (and glancing at my bookshelves), in no particular order, I'm going to suggest a look at Brunelleschi's Dome by Ross King, Shrinking the Cat by Sue Hubbell (history as well as science), Names Through the Ages by Teresa Norman (which has history as well as names, and is great geek fun, in my geeky opinion), Power With Grace by Ishbel Ross (a biography of Mrs. Woodrow Wilson), Hard Bargain by Robert Shogan (FDR and Churchill), John Adams by David McCullough, The Path Between the Seas by David McCullough, (OK, practically anything by David McCullough), Washington Goes to War by David Brinkley, Spies of the Revolution by Katherine and John Bakeless, and New Land, New Lives: Scandinavian Immigrants to the Pacific Northwest by Janet E. Rasmussen (oral histories).
Another regional book with a narrower focus, which is sometimes dry facts and sometimes full of hilarious or odd happenings, is Cornerstone: The formative years of St. Vincent -- Oregon's first hospital by Ellis Lucia. It also has some great old photos, if you like that sort of thing.
For a really geeky entry, there's One Good Turn: A Natural History of the Screwdriver and the Screw, by Witold Rybczynski. Hey, don't laugh. This is about a tool that changed civilization, and its history encompasses more than you might think.
In the same vein, there's The Evolution of Useful Things by Henry Petroski and The Pencil: A History of Design and Circumstance, by the same author. I've long since sold my copies of those, but I seem to remember them as interesting reads.
This list is, admittedly, all over the board as far as subject matter, depth, and style. I hope Krista finds something she likes in it.
But I'm sure she'd like to have your recommendations, too. So would I, for that matter.