From http://codex.wordpress.org/Class_Reference/WP_Query#Custom_Field_Parameters

meta_query.php

<?php 
$args = array(
	'post_type' => 'product',
	'meta_query' => array(
		'relation' => 'OR',
		array(
			'key' => 'color',
			'value' => 'blue',
			'compare' => 'NOT LIKE'
		),
		array(
			'key' => 'price',
			'value' => array( 20, 100 ),
			'type' => 'numeric',
			'compare' => 'BETWEEN'
		)
	)
);
$query = new WP_Query( $args );