I just found a solution that works for me from here: http://www.onedesigns.com/support/topic/added-next-previous-links-to-single-php-2.
But I put the code lower down than this person suggested: after the closing div tag for <div class="entry-content">.
Here is the code that I ended up using:
<div><?php previous_post_link('%link', '«« Previous work');?> | <?php next_post_link('%link', 'Next work »»');?></div>
Hope this helps!
