Eh, I don't think you need a book for Joomla, what with all of the neat extensions they have available. Some of them are worth paying for if you're doing a business website. You get better support and a better app (for the most part, but not true in all scenarios). One Joomla extension that's free that I would recommend is Akeeba Backup. It allows for backup and restoring of your site. There's also template software out there that's called Artisteer that's really good. I've purchased it in the past and it will import and export Joomla and Wordpress templates to work with your site. It's not very expensive either.