http://askville.amazon.com/add-Share-Facebook-button-webpage/AnswerViewer.do?requestId=1539369

Copy the script for the style you’d like:
Copy and paste the following code blocks into your site and replace ” with the link you want to Share.

Text link:

// <a onclick="return fbs_click()" href="http://www.facebook.com/share.php?u=&#8221; rel=”nofollow” target=”_blank”>Share on Facebook

Small icon and text:

// <a class="fb_share_link" onclick="return fbs_click()" href="http://www.facebook.com/share.php?u=&#8221; rel=”nofollow” target=”_blank”>Share on Facebook

Icon only:

// <a class="fb_share_button" style="text-decoration: none;" onclick="return fbs_click()" href="http://www.facebook.com/share.php?u=&#8221; rel=”nofollow” target=”_blank”>Share