List custom taxonomy terms

I believe what you are looking for is the get_terms function. I found it looking at the code for wp_tag_cloud, here is the source of the function. This little snippet should get you what you are wanting.

$terms = get_terms("characters");

if ( empty( $tags ) || is_wp_error( $tags ) )
  return;

foreach ( $terms as $term ) {
  echo $term->name;
}