I am delighted to see that with the interest in Harry Potter the Diana Wynne Jones books are being reissued. I'm collecting them whenever I see one.Philip Pullman is also a lovely author to read. His Golden Compass trilogy is for older readers but my kids are enjoying Count Karlstein which is a great take on the gothic thriller.
Alan Garner's Weirdstone of Brisingamen would also be a good read for any young fantasy readers.