I became a huge fan of Harry Potter when I read the first book in the series in the late 1990s, thanks to my (now) mother-in-law, who lent me her hardcover of Harry Potter and the Sorcerer's Stone. I consequently refaced my bedroom in my parents' house with all things Harry Potter. I'm a little older now, and I no longer live with my parents, but I still await every new Harry Potter book and film with bated breath (though the films are never as good as the books, not surprisingly). I don't read much other children's fiction, but this section also includes young adult fiction that is probably most suitable for teenagers and mature younger readers. I first encountered many of these when I was a young adult myself, and they've been on my keeper shelves since.
Anna to the Infinite Power (1981) (young adult) - a gripping novel about scientific experimentation on human cloning and the Jewish Holocaust that caught a hold of me when I was a kid; check out the 1983 film adaptation as well if you're interested (though it's not as good as the book)
The Silver Metal Lover (1981) (young adult) - a classic young adult story of love...with a robot
Metallic Love (2005) (young adult) - sequel
Margaret Mahy
The Changeover (1974) (young adult) - a teenage girl in a single-mom family, a sick younger brother, an evil vampiric creature sucking the life out of the young for his immortality, and, of course, good witches...I love this book
Sunshine (2003) (young adult) - a wonderfully fresh twist to the beauty-and-the-beast tale: vampires! (or is it a wonderfully fresh twist to the vampire love story?)
His Dark Materials series (young adult) - a simply brilliant series, with a thoughtful, compelling take on religion, spirituality, and the metaphysics of consciousness; the exciting plot and complicated, richly-drawn characters will draw you in
The Golden Compass (1996) [Northern Lights in UK (1995)]