I realize this is rather an odd juxtaposition of books, but bear with me for a minute! When I was in 5th grade my teacher had the rest of the class read My Brother Sam is Dead, during our Revolutionary War unit, but she made me read 8 books. (Clearly, she knew me well.) I remember My Brother Sam is Dead and Johnny Tremain, although I've forgotten some of the others, but Time Enough for Drums is the one that stands out. It just grabbed me for some reason; perhaps because Jemima's spunkiness was irresistible. (I tried pretty hard to talk Noel into the name Jemima when I was pregnant with Eleanor, but he couldn't get over the Aunt Jemima/syrup association.) Anyway, I've never forgotten Time Enough for Drums, and I think it's a big part of why I always have enjoyed Revolutionary War era books, like those of David McCullough or Joseph Ellis.
The Given Day I just read a few years ago, but for some reason it's kind of haunted me. It's set in Boston during the 1910s, and it's such a big novel, with themes of immigration, love, prejudice, war, betrayal, labor, etc, and I find myself mentally referencing it a lot, whenever I read other immigration fiction, or even on Labor Day this year, when I was trying to explain labor unions to Eleanor. It was great on audiobook by the way, if you're thinking of reading it -- the narrator did an awesome job with all the Bostonian and varying Irish accents.
What books do YOU find unforgettable?