post - WordPress built-in post type
page - WordPress built-in post type
attachment - WordPress built-in post type
revision - WordPress built-in post type
nav_menu_item - WordPress built-in post type (Since 3.0)
custom post type - any custom post type (Since 3.0)

I need to ignore the attachment revision and nav menu types which are all returned by $post_types = get_post_types( $args = $excludes ); when there is no excludes. So I can set a flag to only grab custom post types. This excludes post/pages though.