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

Les Harris

The Pressbox plugin adds a new tab to the Media Upload screen that allows you to insert images and files from Dropbox into your posts.
Additionally, the plugin provides a new shortcode that lets you add links or display images anywhere you want on your blog.
This plugin is under heavy development so please feel free to send me feedback, bug reports, and feature requests!
Credits:
This plugin bears a great debt to the work of Joe Doleson’s Wp To Twitter plugin for his excellent example of OAuth integration with WordPress.

Pressbox

Integrates DropBox with your blog allowing you to post images and files directly from your DropBox. Requires PHP 5.2 and cURL.

Dropbox Upload Form vs Pressbox