List of modules by importance
https://groups.drupal.org/node/174769
Drupal Themes Live Demo, Drupalテーマを見て確認できるサイト
http://drupaltheme.octaviadata.com
Drupal based websites
http://topdrops.org/
Drupal Case Studies
https://www.drupal.org/case-studies
showcases
https://www.drupal.com/showcases