After reading Primo Levi's "The Drowned and the Saved", I went on a binge of his earlier works: "If This Is a Man", "The Truce", "If not now, when?". All great, but I keep coming back to "The Drowned and the Saved"; it's hard to put my finger on it, but it's a book that provides more meaning about life than anything I've ever read.
The Periodic Table is also very special, and like the books you mentioned, the surprising part is that it says something additional about his experiences to each of the other books.