As of wordpress 3.8 it’s really simple to add Custom Icons to WordPress Admin. Use Dashicons!

wordpress-dashicons

Dashicons is the official icon font of the WordPress admin as of 3.8.

In your custom post type initialization add the “menu_icon” option.

$args = array(
‘menu_icon’ => ‘dashicons-video-alt3’,
);

There’s a great selection of icons you can use.

wordpress-admin-icons