Some Drupal Modules I've Used

Recently, a fellow Drupalist asked me a really good question, approximately worded: “what are the modules you are familiar.” This is a great question, and I wanted to pick some awe inspiring modules that had a 'wow-factor' but all I could think of was “link,” “devel,” but what I wanted to say was some great module that really did everything and summarized what Drupal is all about.