Harry Potter

Harry Potter is a series of novels by J.K. Rowling.  The main character is an young wizard named Harry Potter.  The series is about the adventures he has while he is a student at Hogwarts.  The series has developed an almost cult-like following.  There are several movies based on the books.  Most library patrons would want to read the books because of their love of the movies, or if they have visited the attraction at Disney World.
The controversial topic in the book is mostly sorcery.  Some parents do not agree with their children reading about sorcery.  I feel that if parents have that strong a belief about their child not reading the book, they must express their thoughts to their child.  It is the child's responsibility to choose what he borrows from the library.  Most non-serious readers will not attempt to conquer the books anyway because of the length.  I feel that if the student is able to read books of that length and reading level, he is mature enough to weigh the consequences of his parents' wishes.

Crank by Ellen Hopkins

Kristina Georgia Snow is an innocent high-school junior who is quiet and doesn't have many friends. When she goes to visit her father, she encounters the drug world and develops an alter-ego named Bree, the opposite of what Kristina used to be like. She meets a guy she falls hard for, and he introduces Bree to the monster, Crank. This book shows the dangers of drug use and how difficult it is to stop using drugs.
Crank is on many lists as controversial for teen readers.  It is loosely based on the author's daughter's life.  The novel deals with drug addiction, teen pregnancy, and rape.  While these issues are controversial, they are real issues that teens face.  The novel does not glamorize any of the problems that the teen faces.  The novel would help teens to see that others are facing the same problems as them.
The novel is written in free verse form which will detract less mature readers.