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.

Scott Grayban

It puts a bar of icons at the bottom of each post allowing your readers to submit your posts to several different 
social networking and bookmarking sites. (del.icio.us, digg, fark, etc.)
The original plugin was called <a href="http://blog.calevans.com/2006/02/08/notable-another-wordpress-plugin/" rel="nofollow ugc">wp-notable</a> 
but no longer worked or was supported. The author was Cal Evans.

notable

Adds social bookmark links to each blog entry.

WP Digg This vs notable