utahta

This plugin inserts social share links at the top or bottom of each post. 
For theme developers, social share links can be added by PHP code or by using shortcode. Check documentation for this use-case.
This plugin documentation can be found <a href="https://github.com/utahta/WP-Social-Bookmarking-Light/wiki" rel="nofollow ugc">here</a>.
This is the list of used social sites:
<ul>
<li>Hatena</li>
<li>Facebook Like Button</li>
<li>Facebook Share Button</li>
<li>Facebook Send Button</li>
<li>Twitter</li>
<li>Tumblr</li>
<li>Google Bookmark</li>
<li>Google +1</li>
<li>Delicious</li>
<li>Digg</li>
<li>reddit</li>
<li>LinkedIn</li>
<li>Instapaper</li>
<li>StumbleUpon</li>
<li>mixi Check</li>
<li>mixi Like</li>
<li>GREE Social Feedback</li>
<li>atode (toread)</li>
<li>LINE</li>
<li>Pocket</li>
<li>Pinterest</li>
</ul>

WP Social Bookmarking Light

This plugin inserts social share links at the top or bottom of each post.

int128

Hatena Star is a recommendation service, popular in Japan.
For details, see Hatena Star documents <a href="http://d.hatena.ne.jp/hatenastar/20070707/1184453490" rel="nofollow ugc">in Japanese</a>, <a href="http://d.hatena.com/hatenastar/20070707/1184453489" rel="nofollow ugc">in English</a>.

WP Social Bookmarking Light vs Hatena Star