Drupal 6

Some examples:

<?php print $title; ?>

<a href="<?php print $node_url ?>"><?php print $title; ?></a>

<?php if (!empty($field_news_image)) {
  print $field_news_image['0']['view'];
} ?>

<\div class="submitted">
    <?php print format_date($node->created, 'custom', 'j F Y'); ?>
</div>

<\div class="field venue">
    <?php print l(($node->field_venue[0]['value']), $node->field_venue_url[0]['value']); ?>
</div>

<\div class="field btn-tickets ticket-link">
  <?php 
    if($node->field_sold_out[0]['Yes']){
      print t('Sold out'); } 
    else {
      print l(t('Tickets'), $node->field_ticket_sales_url[0]['value'], array('class' => 'buy-tickets')); }  
  ?>
</div><?php print $title; ?>

<a href="<?php print $node_url ?>"><?php print $title; ?></a>

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Print the complete CCK Link field:

<?php print $node->field_listing_website[0]['view'] ?>

Or separate the URL from the title:

<?php 
    $link_url = $node->field_link[0]['url'];
    $link_title = $node->field_link[0]['title'];
?>

<div<?php print $node_attributes; ?>>
  <?php if (!empty($link_url)) : ?>
    <a href="<?php print ($link_url); ?>">
  <?php endif; ?>




      <\h2 class="node-title"><?php print $title; ?><\/h2>
    <?php print $content; ?>
  



  <?php if (!empty($link_url)) : ?>
    </a>
  <?php endif; ?>
</div>

This is also explained pretty well here: http://www.caucusllc.com/blog/theming-a-cck-node

Drupal core fields:

<?php print $fields['title']->content; ?>
<?php print $fields['body']->content; ?>
<?php print $fields['nid']->content; ?>

Print the teaser:

<?php print $fields['teaser']->content; ?>

CCK fields:

<?php if ($fields['field_location_value']): ?>
<?php print $fields['field_image_fid']->content; ?>

If a field is optional, you might want to say "if field is not empty", like this:

<?php if (!empty($fields['field_image_fid']->content)) {
  print $fields['field_image_fid']->content; }
?>

Especially if you want to add a div or h2 around the print, like this:

  <?php if ($fields['field_location_value']): ?>
    <div class="sample"><?php print $fields['field_location_value']->content; ?></div>
  <?php endif; ?>
  <?php if ($fields['field_venue_value']): ?>
    <<div class="sample">><?php print $fields['field_venue_value']->content; ?></div>
  <?php endif; ?>

Finally, here's a great tutorial on views row theming from the good folks at Mustardseed Media [source]