Madeleine L'engle's Time Quartet by Madeleine L'Engle (1991, Paperback, Reissue)

While targeted at a younger audience, these books are quite extraordinary in terms of content and style, and can be enjoyed by anyone, just like Robert Heinlein's early books. The books in this quartet are adventures surrounding the unusual Murry family members, and manage to blend in everything from quantum physics to personal relations in an amazingly well-written and entertaining way.

These stories blend fantasy, science, religion, myths and the general issues of daily family life in a very positive way, and are an enjoyable read no matter what your background or age may be. I happened to pick up A wrinkle in time from our bookshelf (it belonged to our kids), and was so impressed, I tracked down the rest of the books to read them, a genuine pleasure.