Epic Alex

<?php $my_query =
new WP_Query('category_name=My Cat&showposts=5');
while ($my_query->have_posts()) : $my_query->the_post();
$do_not_duplicate[] = get_the_ID();?>
<!-- Do Stuff Here -->
<?php endwhile ; ?>

<?php query_posts('category_name=Second Cat&showposts=5'); ?>
<?php while (have_posts()) : the_post();
if (array_search(get_the_ID(), $do_not_duplicate) !== false)
continue; update_post_caches($posts); ?>
<!-- Do Stuff Again -->
<?php endwhile ; ?>