Change this line
$['a'].after(' (' + href + ') ');
to
$('a').after(' (' + href + ') ');
$ should be called as a function, not an array.
Although looking at your code, you probably want this instead:
$(this).after(' (' + href + ') ');
edit:
here is the full code:
$('a[href^="http://"]').each(function(){
var href = $(this).attr('href');
href = href.replace('http://', '');
$(this).after(' (' + href + ') ');
}); // end each