All external links in new window.

gistfile1.js

<script>
    $(document).ready(function() {
        $('a[href]')
            .filter(function(){
                return ($(this).attr('href').match(new RegExp('^https?|ftp')));
            })
            .filter(function(){
                return (! $(this).attr('href').match(new RegExp('^(https?|ftp):\/\/'+location.hostname)));
            })
            .attr('target', '_blank');
    });
</script>