Drupal: Removes all stylesheets except those added by the theme. Should be added to your template.php file. More info can be found here: http://api.drupal.org/api/drupal/modules--system--system.api.php/function/hook_css_alter/7

gistfile1.aw

function THEME_css_alter(&$css) {
  foreach ($css as $key => $value) {
    if ($value['group'] != CSS_THEME) {
      $exclude[$key] = FALSE;
    }
  }
  $css = array_diff_key($css, $exclude);
}