Digital Downloads Dropbox File Store allows you to provide your digital goods through the Dropbox storage / file sharing infrastructure.
By using Dropbox to host your files you will gain the secure, high-availability capabilities provided free-of-charge by Dropbox as well as avoid any extra hosting or transfer fees on your own site.
Digital Downloads Dropbox File Store – how it works:
When using File Store for Dropbox you can use a file on Dropbox in two different ways. The first option is to copy files to Dropbox first and then select them from within the WordPress Insert Media screens. This way you don’t need to worry about any upload limits or file incompatibilities on your WordPress site. The second option allows you to upload files directly from the same WordPress Insert Media window, the same as you do today, and then select those for use. This way you never need to leave your WordPress environment. Either way, File Store for Dropbox supports files in any directory and will automatically expire your download links after a few hours to prevent link sharing.
Note: this extension requires that your site be running PHP 5.3 or later.