Study the Drupal Showcase (drupal.org/forum/25). Browse to see what people are doing and what types of projects they pursue with Drupal. You may want to specifically read the descriptions that often mention how long it took to develop a Drupal site (be prepared to be pleasantly surprised). Then, use the search feature to search the listings for features you are interested in adding to your site.
To find other sites that use Drupal, browse the jobs listings at groups.drupal.org/jobs. Not only will you see the available jobs, but you'll see the companies that are using Drupal and what they are doing with it. Notice, too, the time frames for the projects that are listed.