Custom posts, by custom taxonomy.

loop.php

        <?php
            $categories = get_terms( 'service-category' );
            foreach ( $categories as $category ) {
                $services = new WP_Query(
                    array(
                        'post_type' => 'services',
                        'showposts' => -1,
                        'tax_query' => array(
                            array(
                                'taxonomy'  => 'service-category',
                                'terms'     => array( $category->slug ),
                                'field'     => 'slug'
                            )
                        )
                    )
                );
        ?>
            <div class="service__list-box">
                <h3><?php echo $category->name; ?></h3>
                <ul>
                 <?php while ($services=->have_posts()) : $services=->the_post(); ?>
                    <li><?php the_title(); ?></li>
                <?php endwhile; ?>
                </ul>
            </div>
        <?php
                // Reset things, for good measure
                $services = null;
                wp_reset_postdata();
            }
        ?>