Frankly, if I'm buying a gift for a serious bibliophile, I think a safer bet is a gift card and then a book-related gift.
Here are some of my all-time favorites for library lovers of all ages:
Phantom Tollbooth Sweatshirt - I love this book so much, not only because it's a classic, but because it was one of the few books my dad read aloud to me (it was one of his childhood favorites, plus he has always loved clever jokes and puns). Actually, I need to go reread this book immediately now. (Besides the Phantom Tollbooth, they also have a bunch of other fantastic sweatshirts with literary covers. You can buy them from Amazon as well (and they are Prime eligible!), but they're quite a bit cheaper directly from Out of Print).
Storybook Blocks - Best baby gift ever. I especially like the Eloise set and the Make Way for Ducklings set and the Harry Potter set. Add a copy of the book and, ta-da! Gift done.
Phone and e-Reader Covers - These cases look like your favorite books, both classics and new releases. This Nancy Drew one especially won me over. And this Peter Pan phone case. (Also, I just discovered that she lives in my same town, so. . . obviously we are meant to be friends).
Book Plate Stamps - Whether you lend out your books frequently or just enjoy marking your property, these customized stamps let everyone know who that book belongs to. I love this one and this one. These would make great teacher gifts too.
Book Light - It has nearly 3,000 reviews on Amazon, comes in several colors, clips to everything, and has two lights for ultimate lighting control. Seriously, I need one of these. http://bit.ly/1X9VeQr
Library Card Tote Bag - If, like me, you are always checking out way more books from the library than your weak little arms can hold, you probably need this bag.
Book Map - I am wary of books that have a map in the front, but this map doens't scare me at all. It's loosely based on a real London map, interwoven with fictional parts of London from famous works of adult and children's literature. Overall, it highlights locations from 600 titles (think Dickens, Austin, Dahl, Woolf, Rowling, Bronte, Tolkien, etc) and has a key at the bottom so you know all the titles and authors included. Nerd heaven, right here.
Modern Fairy Tale Prints - If the Disney version isn't your style, these understated designs are just way too cool, with just a touch of the dark undertones most fairy tales originally had. I love Little Red Riding Hood, The Three Pigs, and Mary Poppins (okay, also The Princess and the Pea).
Personal Library Kit - I found this last year when I was researching gift ideas for a different post and I still love it just as much as I did then. You get one of those amazing due date stamps, pockets for putting in your books, and library due date cards that slip into those pockets. This is just basically my dream gift.
Library Due Date Socks - Cozy socks and a good book are the recipe for a happy life, I think.
Mug and Book Saucer - If you, like me, think all books are better with a beverage or food (let's be honest - candy) accompaniment, this mug with a saucer shaped like a book is absolutely delightful.
Book Washi Tape - Washi tape is still going strong (and for good reason: it's cute and useful), but when you add books to it? You know I'm all in.
BabyLit Stroller Cards - You know my love for BabyLit books runs deep and wide, but I also love their collections of other products, including puzzles and games. These stroller cards are fun for playing or make beautiful mobiles or wall displays.
Book Ends - These bookends are just so pretty. Whether you're putting them in a child's room or on your mantle, they are a talking piece for sure, and guaranteed to make your books look even better than they already do.
Library Cart - This is just plain ridiculous, but I would kill for one of these to keep all my library books in (a basket? WAY not cutting it when you're dealing with the kind of book volume our family is). Plus, I just love the way it looks. The Land of Nod sells cute mini-versions, but I have to admit that what I really want is a legit, library-supply-company one. Even more ridiculous? I totally want an old cart catalog cabinet. I have no idea what I'd do with it, but I want one anyway. (One of Bart's parents' friends has one she bought at some school auction and turned into a kitchen island and she uses all the tiny long drawers for kitchen utensils. I covet it every time we visit).
And you know I'd love to see your suggestions for what to buy the book lover in your life (even - or maybe especially - if that book lover is you).