This plugin for wordpress generate a list of users of the current wordpress site according to a user level range. Steve Maranda
UnZip in the plugins directory activate it then set parameters in settings.
This plugin uses jQuery so be sure to have included the library from your theme.
Usage : Simply paste this code in the theme file where you want the list to be displayed. <?php wpul_get_users(); ?>
See http://codex.wordpress.org/User_Levels for levels explanations.