Extract a list of all Organic Groups groups with their names. Works with OG 7.x-2.x - tested with 7.x-2.2.

mymodule.module

<?php

/**
 * Extract a list of all available Organic Groups.
 *
 * This is ugly and inefficient, but it is the only way
 * I could figure out how to do it, but hey it works.
 * 
 * This is designed to work with OG 7.x-2.x
 * 
 * @params array $entity_types
 *   Limit the search to the entity types specified.  All types checked if omitted.
 * 
 * @return array
 *   All of the groups in the site.
 */
function mymodule_get_all_groups($entity_types = NULL) {

  if (NULL === $entity_types) {
    $entity_types = array_keys(og_get_all_group_entity());
  }

  $groups = array();
  foreach ($entity_types as $entity_type) {
    foreach (entity_load($entity_type, og_get_all_group($entity_type)) as $id => $entity) {
      $groups["{$entity_type}__{$id}"] = entity_label($entity_type, $entity);
    }
  }

  return $groups;
}