Plugin Name: Facebook-share
Plugin Description: Add a Facebook Share Button to each post to allow your readers to share your post with their Facebook friends. 
Plugin URL: http://wiki.developers.facebook.com/index.php/Fb:share-button
Author: Dog Lover
Author URL: https://www.intensedebate.com/people/doglover2688
Date Added: September 15th, 2009

Code:
function add_fb_share() {
var fb_link = document.createElement('a');
fb_link.href = 'http://www.facebook.com/share.php?u=' + window.location.href;
fb_link.className = 'fb_share_button';
fb_link.onclick = 'return fbs_click()';
fb_link.target = '_blank';
fb_link.style.textDecoration = 'none';
fb_link.innerHTML = 'Share';
fb_link.style.cssFloat = 'right';
document.getElementById('idc-container').insertBefore(fb_link, document.getElementById('idc-container').firstChild);
}

function fbs_click() {
u=location.href;
t=document.title;
window.open('http://www.facebook.com/sharer.php?u='+encodeURIComponent(u)+'&t='+encodeURIComponent(t),'sharer','toolbar=0,status=0,width=626,height=436');
return false;
}
id_add_action( 'idcomments_func_load', add_fb_share);

CSS:
#idc-container .fb_share_button { display: -moz-inline-block; display:inline-block; padding:0 !important; height:18px; width: 57px; background:url(/images/facebook-share-icon.gif) no-repeat top left; text-indent: -9999999px; margin-left: 5px; cursor: pointer; }