To know what theme functions are available
The default theme implementations for Drupal core can be found listed here:

http://api.drupal.org/api/drupal/modules%21system%21theme.api.php/group/themeable/7

If you want the theme functions for contrib as well, you could use hook_theme_registry_alter on your install and dump out the theme registry with devel to list all the theme implementations.

e.g

/**
 * Implements hook_theme_registry_alter
 */
function mymodule_theme_registry_alter(&amp;$registry){
  dpm($registry); // requires devel module
}