The American Library Association is the main sponsor of Banned Books Week. Their website provides ideas on how to celebrate the annual event in your community or school, lists of frequently banned books, and resources for fighting a local challenge "A challenge is an attempt to remove or restrict materials, based upon the objections of a person or group. A banning is the removal of those materials. Challenges do not simply involve a person expressing a point of view; rather, they are an attempt to remove material from the curriculum or library, thereby restricting the access of others. As such, they are a threat to freedom of speech and choice."
"Banned Books Week was launched in 1982 in response to a sudden surge in the number of challenges to books in schools, bookstores and libraries. More than 11,300 books have been challenged since 1982." With separate sections of resources for kids, librarians, teachers, parents, students, writers, booksellers and artists, this is another American Library Association website, created in association with about a dozen other official sponsors. Be sure to visit their YouTube page to view videos of readers reading from their favorite banned or challenged book.
Comic books are also frequently challenged, but I was surprised to learn about the existence of the Comic Book Legal Defense Fund. It is a non-profit "dedicated to the protection of the First Amendment rights of the comics art form." Jump to Resources for articles on why comic books are banned, which comics are frequently challenged, and the history of comic book bans. "Comic books have been the object of legal controversy since the 1950s when the Senate Judiciary Committee's Subcommittee to Investigate Juvenile Delinquency investigated the medium in response to public pressure about its content."
The National Coalition Against Censorship (NCAC) offers support and advocacy for those fighting book challenges. The Kids' Right to Read Project specifically offers "advice and assistance to students, teachers and others opposing book-banning in schools and communities nationwide." To learn more about the organization, read up on their position against book ratings (you'll find the link in the third paragraph.) "The KRRP has spearheaded a collaborative effort to oppose the growing trend to rate and label books, like movies and video games."
The S-Collection from the library at University of Illinois at Urbana-Champaign offers lists of frequently banned children's books in three categories: Picture Books, Chapter Books, and Young Adult Books. For example, in the Picture Book category you'll find "Where's Waldo," "Where the Wild Things Are," and "Strega Nona." The site also provides a short list of sources for additional research, but a few of these require campus credentials (and are not available to the public.)