Also, you can find a lot of articles on this topic out there. Here's one on the book Jen was showing around at the beginning of class:) I encourage you to be creative (there is no real "border" with controversial books. Please include in your post 1) your thoughts of why this picture book might be considered controversial and 2) whether you are comfortable teaching the book to children. If not, why not? Which grade levels would you recommend the book for?
Here are a few more suggestions (hat tip to Lewis).
HIROSHIMA, NO PIKA, by Toshi Maruki
WHITE WASH, by Ntozake Shange
NAPPY HAIR, by Carolivia Herron
FLY AWAY HOME, by Eve Bunting
SMOKY NIGHT, by Eve Bunting & David Diaz
FRIENDS FROM THE OTHER SIDE, by Gloria Anzaldua
ROSE BLANCHE, by Christopher Gallaz & Roberto Innocenti
FAITHFUL ELEPHANTS: A TRUE STORY OF ANIMALS, PEOPLE, AND WAR, by Yukio Tsuchiya
SAMI AND THE TIME OF TROUBLES, Judith Heide