DZVO

This plugin allows you to display a buttons which shows the voting for a social news message (digg,sphinn …) on your blog post. 
You will find a collection of voting buttons for different social-news-services <a href="http://www.zauberpage.de/vote-it-liste.html" rel="nofollow ugc">here</a>.

Vote It!

Vote It! Buttons for Blogpostings. Set very simple a digg, sphinn or another social-news-button in your blogpost.

Vladimir Prelovac

WP Digg This is a plugin that adds a Digg button, but with a twist. Instead of adding a Digg button to all your posts, WP Digg This plugin selectively adds the button only to posts you want.
To add a digg button just add a ‘digg’ custom field with value ‘1’.
WP Digg This can display digg button on your single pages but there is an option to show them on home and archive pages as well.
Plugin by <a href="http://www.prelovac.com/vladimir" rel="nofollow ugc">Vladimir Prelovac</a>.
<h3>License</h3>
This file is part of WP Digg This.
Category Search is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
Category Search is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with Category Search. If not, see <a href="http://www.gnu.org/licenses/" rel="nofollow ugc">http://www.gnu.org/licenses/</a>.

WP Digg This

Provides an easy way to selectively add Digg button to your posts. Use 'digg' = '1' custom field in the post to promote it.

Vote It! vs WP Digg This