Can't get template suggestions to be recognized
It took me a bit to figure this out and what I came up with is that the issue appears to be that Drupal's Theme System will only look for dynamic templates if they are in an actual theme, not in with a module.

So, you can do one of two things, the first one obviously being to copy all of your facet-item templates into your theme directory and call it a day after clearing caches for Drupal to pick them up.

Or... you could get creative like the Views Module does and create theme registry hooks for each of the template files like so:

function dsfacet_theme($existing, $type, $theme, $path) {

  $hooks=array();
  $modulepath = drupal_get_path('module', 'dsfacet');

  $hooks['facet_item']= array(
    'variables' =&gt; array('facet_name' =&gt; NULL, 'facet_values' =&gt; array()),
    'pattern' =&gt; 'facet_item__',
    'template' =&gt; 'facet-item',
    'path' =&gt; $modulepath . '/tpl/facet-items',
  );

  $hooks += drupal_find_theme_templates($hooks, '.tpl.php', $hooks['facet_item']['path']);
  // $hooks += _views_find_module_templates($hooks, $hooks['facet_item']['path']);

  return $hooks;

}


which if you have Views installed will actually use Views' _views_find_module_templates() function to do all the work for you. (it basically goes through the directory passed to it and looks for template files and creates $hooks['facet_name__foo'] for each one it finds.) If you don't have or want Views installed, you can just copy it out of views.module and include and rename it accordingly in your own module.

ADDITION/CORRECTION:  DUH; YOU CAN USE drupal_find_theme_templates() just as easily without worry about using/including Views' similiar private implementation.

And now if you have put all your facet-item templates under your module in their own directory structure (mostly so the find template function doesn't find any other templates and spin its wheels doing extra work) and cleared caches, you should now see all of your templates.