NeutralAxis

The basic format for Facebook is this.

<br/><a href="http://www.facebook.com/sharer.php?t=Title of Post&u=http://URL_of_post"><img src="facebook_icon.png" alt="Facebook Share" /></a>

You can automate the title of the post and the URL like this.

<br/><a href="http://www.facebook.com/sharer.php?t=<?php the_title(); ?>&u=<?php the_permalink() ?>"><img src="facebook_icon.png" alt="Facebook Share" /></a>

And in my case where I’m using the YOURLS plugin to generate short URLs, I can further automate the URL to be the short URL.

<br/><a href="http://www.facebook.com/sharer.php?t=<?php the_title(); ?>&u=<?wp_ozh_yourls_raw_url(true); ?>"><img src="facebook_icon.png" alt="Facebook Share" /></a>

Place that in your single post and/or page template and it will send the user to twitter where they’ll be asked to log in, and then the post title and short url are prepositioned for them.  Of course, you’ll also need to adjust the icon filename as needed for your specific case.