'A Song of Ice and Fire' series by George R.R. Martin is also a great choice. With its large cast of characters, complex political intrigue, and a world full of magic and mystery, it has a lot in common with what fanfiction offers. There are so many storylines and characters that it's easy to see why it would attract those who enjoy fan - created content.
Another good one is 'Anne of Green Gables' by L.M. Montgomery. The story of Anne Shirley is full of charm and her vivid personality can be quite inspiring for those who like to create their own stories in fanfiction. The bucolic setting and the relationships she forms with the people around her are elements that can appeal to fanfiction fans.