Marcus Sedgwick is one of the great un-read, has some terrific books already in publication and across such a broad range of subject matter that you really should give his work a try.
He works for a children's publisher by day, and many of his books are in the children's sections but I am 48 and love the children's books just as much as his older material. When I buy a book I the shop will always tell me that there are just as many older readers buying as there are children.
I would thoroughly recommend the Book of Dead Days/Dark Flight Down stories, a complete fantasy escape; and Blood Red, Snow White - a fusion of Russian folk tales and the doomed love story of author Arthur Ransome and his Russian mistress during the Revolution.
Any other fans out there?
When much is taken, something is returned.