efficient_wp_list_authors doesn't rape your server: http://core.trac.wordpress.org/ticket/5407

functions.php

<?php
function efficient_wp_list_authors($args = '') {
  global $wpdb;

  $defaults = array(
    'optioncount' => false, 'exclude_admin' => true,
    'show_fullname' => false, 'hide_empty' => true,
    'feed' => '', 'feed_image' => '', 'feed_type' => '', 'echo' => true,
    'style' => 'list', 'html' => true
  );

  $r = wp_parse_args( $args, $defaults );
  extract($r, EXTR_SKIP);
  $exclude_admin = $exclude_admin ? "WHERE user_login <> 'admin'" : ''; 
		
  $return = '';

  /** @todo Move select to get_authors(). */
  $users = get_users_of_blog();
  $author_ids = array();
  foreach ( (array) $users as $user )
    $author_ids[] = $user->user_id;
  if ( count($author_ids) > 0  ) {
    $author_ids = implode(',', $author_ids );
    $authors = (array) $wpdb->get_results(" 
        SELECT $wpdb->users.ID, user_nicename, display_name, COUNT($wpdb->posts.ID) AS posts 
        FROM $wpdb->users " . (!$hide_empty ? 'LEFT' : '') . " JOIN $wpdb->posts 
                ON  $wpdb->posts.post_author = $wpdb->users.ID AND post_type = 'post' AND " . get_private_posts_cap_sql( 'post' ) . " 
        $exclude_admin 
        GROUP BY post_author 
        ORDER BY display_name"); 
  } else {
    $authors = array();
  }
  if ( empty($authors) ) return false;
  
 
  
  if ( $show_fullname ) { 
    $user_ids = $wpdb->get_col(null); 
  	$link = '';

    $meta = (array) $wpdb->get_results(" 
      SELECT user_id, meta_key, meta_value 
      FROM $wpdb->usermeta 
      WHERE user_id IN (" . join(',', $user_ids) . ") AND (meta_key = 'first_name' OR meta_key = 'last_name') 
      ORDER BY meta_key, meta_value, user_id"); 

    $user_meta = array(); 
      foreach ($meta as $v)
        $user_meta[$v->user_id][$v->meta_key] = $v->meta_value; 
  }
  foreach ($authors as $author) { 
    $name = $author->display_name; 
    if ( $show_fullname && !empty($user_meta[$author->ID]['first_name']) && !empty($user_meta[$author->ID]['last_name']) ) 
      $name = trim($user_meta[$author->ID]['first_name'] . ' ' . $user_meta[$author->ID]['last_name']); 


    if ( $hide_empty && 0 == $author->posts ) { 
   	  $return .= '<li>' . $name . '</li>'; 
      continue; 
    } 
    $return .= '<li>'; 
    $link = '<a href="' . get_author_posts_url($author->ID, $author->user_nicename) . '" title="' . sprintf(__("Posts by %s"), attribute_escape($author->display_name)) . '">' . $name . '</a>';

    if ( (! empty($feed_image)) || (! empty($feed)) ) { 
      $link .= ' '; 
      if (empty($feed_image)) 
        $link .= '('; 
      $link .= '<a href="' . get_author_rss_link(0, $author->ID, $author->user_nicename) . '"'; 
      
      if ( !empty($feed) ) { 
        $title = ' title="' . $feed . '"'; 
        $alt = ' alt="' . $feed . '"'; 
        $name = $feed; 
        $link .= $title; 
      }
      $link .= '>'; 
      if ( !empty($feed_image) ) 
        $link .= "<img src=\"$feed_image\" border=\"0\"$alt$title" . ' />'; 
      else 
        $link .= $name;
      $link .= '</a>';
      if ( empty($feed_image) )
        $link .= ')';
    }
    if ( $optioncount ) 
      $link .= ' ('. $author->posts . ')'; 
    $return .= $link . '</li>';
  }
        
  if ( ! $echo )
    return $return;
  echo $return;
}
?>