If you'd like to see the lists of most frequent challenges, you can find it here thanks to the American Library Association. The link also shows a list of the most common reasons why a book is challenged. The ALA's website has a ton of information about banning and challenging books, and there's a list of events in honor of Banned Books Week.
I'm going to tell another very personal story now, one that doesn't necessarily have to do with banning or restricting access to books, but one that I still think fits with the idea of Banned Books Week. I may not be a widely published author, but even I've been banned.