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.

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.

Vote It! vs notable