I'm a big fan of Terry Pratchett's work. I also enjoyed Mark Haddon's "The Curious Incident of the Dog in the Night-Time."
I had to read that book in english when I still was in High School. I myself got an A on the test we did afterward, however a friend of mine didn't even get a grade, just the question "Did you actually read the book?".
Anyway, it is a good book.