Coming up on the holiday season, I want to put in a plug for "A Christmas Carol" by Charles Dickens. I re-read it during Christmas week every year, and sometimes I also watch my favorite movie version, which is the one casting Patrick Stewart (from Star Trek and X-Men fame) as Scrooge. (He did a one-man audio recording of the book that is excellent as well.)
My favorite all-time book (also one that I re-read regularly) is "The Phantom Tollbooth" by Norton Juster. I'm now in my forties; I have had this book and read it since I was a child, and have come to enjoy it more and more over the years. It's one of those witty children's books that is actually an allegory with a lot of intelligence and humor that will pass right over the heads of a juvenile reader. Those of you who have school age children may enjoy reading it with them.
Another classic fiction book that hasn't been mentioned yet is "The Princess Bride," by William Goldman. The 80s movie based upon it is excellent and is well worth watching as well, but (as with most things), the book is better.
For nonfiction, my favorite book is Thomas Stanley's "The Millionaire Next Door." It came out right around the time I got out of college and has had a lasting impact on me. Definitely higher yield for those of you who are still youngish and in school, but still worth reading (or re-reading) even for those of us who are a bit more "mature."
A newer but excellent book that I read recently for those who like science is Sidhartha Mukerjee's "The Gene." This is the same physician who wrote "The Emperor of All Maladies," and his new book is a prequel of sorts to that book in that it discusses the "normal" of genetics.
I also really enjoyed "The Moral Arc" by Michael Shermer, which gave me a lot to think about in terms of how, over the whole span of millennia, and in spite of the fact that there is still a lot of room for improvement, we really have come quite a long way as a species in terms of our moral development and critical thinking abilities. Good book to read in that it offers an optimistic view on humanity's development to counter all those who think we're flushing ourselves (the planet, the economy, whatever) down the toilet.