List posts AND custom post type by category

I found this answer on the WordPress forum to be of help:

http://wordpress.org/support/topic/custom-post-type-posts-not-displayed?replies=5#post-2805344

basically, the poster references a post by Justin Tadlock (who is pretty much an authority in WordPress theme and plugin desing by the way. Follow his blog if you want to get savvy on WordPress.)

http://justintadlock.com/archives/2010/02/02/showing-custom-post-types-on-your-home-blog-page

In his blog post he provides a code snippet that you can add to your functions.php page:

add_filter( 'pre_get_posts', 'my_get_posts' );

function my_get_posts( $query ) {

    if ( is_home() && $query->is_main_query() )
        $query->set( 'post_type', array( 'post', 'page', 'album', 'movie', 'quote' ) );

    return $query;
}

and this seems to work fairly well. Of course, you might want to change is_home() to is_archive() and substitute album, movie, quote for your custom post type handles as you’ve registered them with the register_post_type function.