Catherine Morland and Henry Tilney from Northanger Abbey by Jane Austen. I'm such a sucker for couples who bond over books, and these two definitely do that!
Hermione Granger from the Harry Potter books by J.K. Rowling. She's a very powerful witch, and reading and remembering what she's read are Hermione's superpowers.
Margaret Hale and Mr. Thornton from North and South by Elizabeth Gaskell. These two don't discuss books much, but they both love reading them and learning from them.
Mary Russell from The Beekeeper's Apprentice and the rest of the series by Laurie R. King. If Mary hadn't had her nose stuck firmly in a book, she might not have stumbled so literally across Sherlock Holmes. She's a scholar, spends many memorable hours in the great Bodleian Library at Oxford, and often uses book research to solve mysteries.
Nero Wolfe from the Nero Wolfe books by Rex Stout. Wolfe's appetite for books is only rivaled by his appetite for food. I love how grumpy he gets over badly written books, but how pleased he can be by a well-written one.