The Golden Compass (1995, in Britain Northern Lights)
The Subtle Knife (1997)
The Amber Spyglass (2000).
I'd hesitate to call this brilliant fantasy series children's literature, as it seems to be received (the library copies I've read have bright, fluorescent green stickers that read "Teen"). Early on, you get brilliant descriptions of cultures that practice trepanation, and the books never seem to condescend. Pulman assumes that the reader, of whatever age, is going to be able to learn about this world akin to ours but so radically different.
The first book starts with Lyra, in Oxford, and her world changing around her. Children are disappearing, and Lyra is taken away from the College in which she grew up by Mrs. Coulter. She runs away, and is swept up with gypsies, and the story swirls through the remainder of the book and throughout the next two. The fantasy world revolves around the idea of many worlds, separated only slightly, and transitions between the various worlds. The story swirls around Lord Asriel, seemingly Lyra's uncle, who makes war on the Authority who is running the world. Describing the story, I feel the urge not to give anything away, and so I can't speak in more than generalities.
It's an incredibly well-written series. The allusions to Paradise Lost seem endless, but the story is clever, well-structured, well-told. The idea that the story is anti-Christian is patently ludicrous. There's a brilliant moment that I'll share that I'm still thinking about, about the nature of faith:
He closed the book.
"And that was how sin came into the world," he said, "sin and shame and death. It came the moment their daemons became fixed."
"But..." Lyra stuggled to find the words she wanted: "but it en't true, is it? Not like chemistry or engineering, not that kind of true? There wasn't really an Adam and Eve? The Cassington Scholar told me it was just a kind of fairy tale."
"The Cassington Scholarship is traditionally give to a free-thinker; it's his function to challenge the faith of the Scholars. Naturally he'd say that. But think of Adam and Eve like an imaginary number, like the square root of minus one: you can never see any concrete proof that it exists, but if you include it in your equations, you can calculate all manner of things that couldn't be imagined without it."
(The Golden Compass 327)
Read these three books. They're well worth the time.