During the recent book update, we needed to make some room for the new WordPress-3.1 content. The book is already over 400 pages and growing. So we have to make some hard decisions about which content is useful but maybe not needed in the book. And, as useful as long lists of anti-spam plugins might be, moving them from the book to the blog seems like a good way to free up some room while keeping the information available. So without further ado, here is a quick list of 15 anti-spam plugins to help you run a more user-friendly, hassle-free comment system.