George Orwell, Animal Farm -- Powerful work in a simple style ponders what happens after the animal revolution.
Phillip Pullman, The Subtle Knife -- A fantasy trilogy following a complex herione. Its popularity in the UK led to the author being invited to a public discussion of the subject matter with Archbishop Rowan Williams.
William Shakespeare -- Any of his plays are classics, and people allude to his beautiful language even when they don't mean to.
Chinua Achebe, Things Fall Apart--This accessible novel is the beginning of the English language African response to imperialism. It's an important link to world history and culture.