Here's the ALA's list of the top 10 most challenged books of this century so far:
The Harry Potter series by J.K. Rowling
The Chocolate War by Robert Cormier
The Alice series by Phyllis Reynolds Naylor
Of Mice and Men by John Steinbeck
I Know Why the Caged Bird Sings by Maya Angelou
Fallen Angels by Walter Dean Myers
It's Perfectly Normal by Robie Harris
The Scary Stories series by Alvin Schwartz
The Captain Underpants series by Dav Pilkey
Forever by Judy Blume
There was always a minority afraid of something, and a great majority afraid of the dark, afraid of the future, afraid of the past, afraid of the present, afraid of themselves and shadows of themselves.
-Ray Bradbury, "Usher II," The Martian Chronicles