PResponsive

This plugin will add a image below your posts, allowing your visitors to share your posts with their friends, on FaceBook, Pinterest, Google+, Twitter, Myspace, Friendfeed, Technorati, del.icio.us, Digg, Google, StumbleUpon, and other. After plugin is activated a buttons will appear after the content of the post.Clicking this button will bring the user to the bookmarking site. If the user isn’t logged in they will be prompted to do so. 
Post your articles to the social bookmarking sites and get traffic.

WP Social Bookmarking

WP Social Bookmarking plugin syndicates your blog posts in social networking sites.

This plugin automatically add links on your posts to popular social bookmarking sites. 
It is an enhanced version of Peter Harkins Sociable plugin.
<h4>Supported Bookmarking Services</h4>
100 social bookmarking services are included! Supported services are:
Ask, BarraPunto, BlinkList, Bloglines, Blogosphere News, Blogsvine, Book.mark.hu, Colivia, DZone, De.lirio.us, Design Float, Digg, DotNetKicks, Facebook, Fark, Folkd, Furl, Gamebuzz, Global Grind, Google Bookmarks, Gwar, Haohao, HealthRanker, Hemidemi, Hype, Internetmedia, Kirtsy, Klickts, LinkaGoGo, Linkarchiv, Linkarena, LinkedIn, Linkter, Live-MSN, Lufee, Meneame, MisterWong, Mixx, MyShare, MySpace, MyTagz, N4G, Netscape, Netselector, Netvouz, NewsVine, Newsrider, NuJIJ, Oneview, Print, Ratimarks, Readster, Reddit, Rojo, SEOigg, SalesMarks, Scoopeo, Segnalo, Simpy, Slashdot, Smarking, Social-Bookmarking.dk, Socializer, Socialogs, SphereIt, Squidoo, StumbleUpon, Technorati, ThisNext, Twitter, Upnews, VoteForIt, Webbrille, Weblinkr, Webnews, Webride, Wikio, Wikio DE, Wikio ES, Wikio FR, Wikio IT, Wikio UK, Wists, Wykop, XING, Xerpi, Y!GG, YahooBuzz, YahooMyWeb, blogmarks, blogtercimlap, co.mments, connotea, del.icio.us, eKudos, email, feedmelinks, newskick, scuttle, seekXL

Sociable Zyblog Edition

Automatically add links on your posts to popular social bookmarking sites.

WP Social Bookmarking vs Sociable Zyblog Edition