I think a great plugin would be a book review request plugin, kind of like http://booksneeze.com/ - where readers can log in and request a book. Authors can list their book to be reviewed. Then once readers submits their review they can request another book by another author.
I think this would be great for Wordpress, and even multisite blogs. :slight_smile:
P.S. Your products are great! Thanks for the sale. :slight_smile: