Dunno if this has been posted before, but I thought it useful enough to pass along this small function. I found the raw code on the 'Net and nade it into a function which I now incorporate in every Wordpress site I build. Allows you to specify custom CSS on a per post or page basis using the built-in Wordpress custom fields. Enter "css" (without the quotes" in the Name field and your custom CSS in the Value field. Wordpress will automatically apply the CSS.
function my_custom_css() {
global $post;
$css_key = get_post_meta($post->ID, 'css', true);
if (!empty($css_key) && is_page()) {
echo '<style type="text/css" media="screen">'. get_post_meta($post->ID, 'css', true) . '</style>';
}
}
add_action('wp_head', 'my_custom_css');
?>
Enjoy!