How can I exclude $(this) from a jQuery selector?

Try using the not() method instead of the :not() selector.

$(".content a").click(function() {
    $(".content a").not(this).hide("slow");
});

You can use the not function rather than the :not selector:

$(".content a").not(this).hide("slow")

You can also use the jQuery .siblings() method:

HTML

<div class="content">
  <a href="#">A</a>
  <a href="#">B</a>
  <a href="#">C</a>
</div>

Javascript

$(".content").on('click', 'a', function(e) {
  e.preventDefault();
  $(this).siblings().hide('slow');
});

Working demo: http://jsfiddle.net/wTm5f/