Add link on the top menu of the post table?

They are filtered via the views_[screen-id] filter. The screen-id of the edit post page is edit-post, so you can modify the links like this:

add_action( 'views_edit-post', 'wpse17484_views_edit_post' );
function wpse17484_views_edit_post( $views )
{
    $views['wpse17484'] = '<a href="https://wordpress.stackexchange.com/questions/17484/my-url">My action</a>';
    return $views;
}

You can see the code that generates the post views in WP_Posts_List_Table::get_views().