The Quickfile module allows instant selling and download of digital products such as ebooks, photographs, music and software. Clients don't need to be registered to buy and they are sent to a page with a link to start downloading right after making their payment.
The file module in the Ecommerce package is quite helpful and I'm thankful for many ideas and code I got from there, but I've noticed that in many sites clients get a little lost when they need to register a Drupal account, wait for a confirmation email and then login and go to "My Files" page to get their files. This can reduce the sales of ebooks.
The Quickfile module creates a new node type called 'quickfile'.
With the Quickfile module clients just need to visit three web pages, when using a credit card, in a single session to make the payment and download a file.