nowadays, joomla is one of the best CMS i've ever meet.. for me personally, i suggest you using joomla.. also great for ebook selling as you can use many plugin that can handle payment.. If you're about to use it, try to use plugin called virtuemart.. Try to do a little search on it..
Magento is really good but a big resource hog. OScommerce and ZenCart are oldSchool-Scripts that do the work but are pain in the ass to customize and upgrade. Joomla + virtuemart is also a good cms+cart combination but i have no good feelings with Joomla's security Check prestashop (prestashop.com) for a pure cart-Script. It is relative new but is realy lightweight and has a fast growing community. My personal Favorite is Drupal (drupal.org) in combination with ubercart (ubercart.org) for a powerful CMS+Commerce solution.
I'm thinking of this too and I am trying to choose between Joomla and Wordpress. Wordpress has a membership plugin called wp-member and I am checking if it meets my needs-- it needs some creativity though. I would like to offer a pay per download and membership access. Will joomla work on this project?
If you guys are talking about some way your ebook gets sold and downloaded check out e-junkie. I looked at all kinds of solutions and have found e-junkie to be the easiest, fastest and cheapest. I run it to sell my ebook: "Survive the Global Crisis" and it really works like magic Oh and you know what's best it even has an affiliate program creator so that it manages your affiliate sales!!!!
hi giorgioarmani -- speaking of e-junkie, I'm thinking of integrating that with Wordpress and wp-member-- I'll surely post on this thread once I started working on it