If you want some controversial stuff, check these themes out:
Politics (Utopias/Dysutopias)-
1984 by George Orwell
Animal Farm by George Orwell
Brave New World by Aldous Huxley
Does This School Have Capital Punishment by Nat Hentoff
Lord of the Flies by William Golding
The Handmaid's Tale by Margaret Atwood
The Giver by Lois Lowry
Gathering Blue by Lois Lowry
Messenger by Lois Lowry
Censorship-
Fahrenheit 451 by Ray Bradbury
The Day They Came to Arrest the Book by Nat Hentoff
Memoirs of a Bookbat by Kathryn Lasky
Discrimination (Racism, Anti-semitism, etc.)-
The War Between the Classes by Gloria D. Miklowitz
The Wave by Todd Strasser
Prank by Kathryn Lasky
Pageant by Kathryn Lasky
Blood Secret by Kathryn Lasky (historical fiction)
Beyond the Burning Time by Kathryn Lasky (historical fiction)
The Witch of Cologne by Tobsha Learner (historical fiction)
The Witch of Blackbird Pond by Elizabeth George Speare (historical fiction)