Different style when listing nodes and displaying a single node
Berdir's suggestion (coolest imho):


  you can even provide custom template suggestions based on the view mode. See for example drupal.org/node/223440 and bri-space.com/content/creating-drupal-template-suggestions


Also within node-article.tpl.php you can inspect $view_mode and decide what to do. You could either include the logic of both templates in the one file, or create different templates and include the appropriate one based on the value of $view_mode

You might also find Display suite interesting.