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.

Chris Klosowski

Allows you to upload your themes CSS, JavaScript, and Images into your Dropbox ‘Public’ folder and server these files from the Dropbox network, reducing the bandwidth of your server and allowing users to load your site faster. Please note that as of now, this plugin only supports themes who use the filters ‘template_directory’, ‘template_directory_uri’, ‘stylesheet_directory’, and ‘stylesheet_directory_uri’ to determine the paths to the theme’s template and stylesheet files. I would only suggest this plugin for users who aren’t afraid of getting their hands a little diry.
This plugin is in no way affiliated with Dropbox.

Dropbox CDN

Use your Dropbox 'Public' folder as a free Content Delivery Network (or CDN). Please read the full description.

XM-Backup vs Dropbox CDN