I always give a lot of books because I have found that I am pretty good at giving books.
For father I picked up Motherless Brooklyn because father is from Brooklyn and a fan of Hammett, Chandler and the like. The fact that father may soon be motherless played no role in my selection and I was pleased that he did not ask whether it had. I also gave him The Great Escape: Nine Jews Who Fled Hitler and Changed the World because it has become something of a tradition for me to give the man a book with Hitler in the title every Christmas. I then purchased Absurdistan because, while he is something of a Holocaust scholar, father does enjoy funny stuff.
For mother I picked up a pair of George Pelecanos novels, Hard Revolution and The Night Gardener. Pelecanos is no doubt a little grittier than what mother is used to, but he writes and produces for The Wire and mother loves The Wire. Also gave her Black Swan Green, Blood Meridian, The Beggar Maid and No One Belongs Here More Than You because she'll dig 'em.
For brother I got The Best American Nonrequired Reading 2007 because it's just about the only book you can get the guy to read. Must be something about that title. Forever the iconoclast, brother apparently delights in making this yearly offering his only required reading.
For brother and girlfriend, two foodies nonpareil in my social circle, I picked up a smörgåsbord of books: The Ethics of What We Eat, The Tummy Trilogy and The New Yorker Book of Food and Drink. To give a foodie a book on the ethics of food seems a bit like giving a sports fan a book on the meaninglessness of sports. "Yeah, yeah, I get it. Now lemme go enjoy my veal chop/ballgame in peace." Nevertheless, I hope they read it.