WordPress: How to Query Posts by Custom Fields

List all posts that have a specific value (example.com, in this example) in a custom field (Fixed Banner URL, in this case):

<?php 
$posts = query_posts( array(
    'meta_query' => array(
        array( 
            'key' => 'Fixed Banner URL',
		'value' => 'example.com'
        )
    )
) );

if( $posts ): ?>
	<ul>	
		<?php foreach( $posts as $post ): 
			setup_postdata( $post );
			?>
			<li>
				<a href="<?php the_permalink(); ?>"><?php the_title(); ?></a>
			</li>
		<?php endforeach; ?>
	</ul>
	<?php wp_reset_postdata(); ?>
<?php endif; ?>	

List all posts that have a value in a custom field (Fixed Banner URL, in this case), whatever the value (list them all):

<?php 
$posts = query_posts( array(
    'meta_query' => array(
        array( 
            'key' => 'Fixed Banner URL',
		'value' => array(''),
		'compare' => 'NOT IN'
        )
    )
) );

if( $posts ): ?>
	<ul>	
		<?php foreach( $posts as $post ): 
			setup_postdata( $post );
			?>
			<li>
				<a href="<?php the_permalink(); ?>"><?php the_title(); ?></a>
			</li>
		<?php endforeach; ?>
	</ul>
	<?php wp_reset_postdata(); ?>
<?php endif; ?>			

List all posts that have a value in a custom field (Fixed Banner URL, in this case), which includes ‘test’ in the value (not exact, just somewhere in the URL):

<?php 
$posts = query_posts( array(
    'meta_query' => array(
        array( 
            'key' => 'Fixed Banner URL',
            'value' => 'test',
            'compare' => 'LIKE'
        )
    )
) );

if( $posts ): ?>
	<ul>	
		<?php foreach( $posts as $post ): 
			setup_postdata( $post );
			?>
			<li>
				<a href="<?php the_permalink(); ?>"><?php the_title(); ?></a>
			</li>
		<?php endforeach; ?>
	</ul>
	<?php wp_reset_postdata(); ?>
<?php endif; ?>