ostlund

This plugin lets you insert a upload form on your pages so visitors can upload files to a Dropbox account.

Dropbox Upload Form

Inserts a upload form for visitors to upload files to a Dropbox account

Xavier Media

This plugin will do a backup of your WordPress database and, or your files in wp-content/uploads and saves 
it somewhere safe. You can have the backup saved in your <a href="http://db.tt/9Jo39Xy" rel="nofollow ugc">Dropbox account</a>, a FTP account of your choise, your 
account with <a href="http://www.securepaynet.net/email/online-file-storage.aspx?ci=1796&prog_id=xaviermedia&isc=xmbackup" rel="nofollow ugc">Online File Folder</a>, or have the backup emailed to you (not recommended for large files). You can 
select to have the backups named the same every day or to have a date added to each file name.
This plugin requires PHP, cURL, PHP compiled with ZIP support, and Oauth (for Dropbox).
** NO WARRANTY SUPPLIED! **
** Make sure you test your Backups! **

XM-Backup

Does a backup of your Wordpress database and, or your files in wp-content/uploads and saves it in a safe location.

Dropbox Upload Form vs XM-Backup