Short FAQ on the topic:

Q: Which sites can be added?
A: You may add any site currently powered by open source content management system Drupal.

However, it is not in our policy to list sites with excessive adult, inflammatory or abusive content.

Q: How do I add my site?
A: Create an account with Drupal Sites Network (it's absolutely free). Just be sure you are logged in. You may use your Drupal.org login credentials as well. Please note that there are some minor miscommunication spotted time to time between drupalsites.net and drupal.org authentication services. If you can't login with your drupal.org account just wait for an hour or a bit more and try again.

Q: What information do I have to submit?
A: Your Drupal site title, url, screenshot (highly recommended) and a short description for your project. Submissions in any language are absolutely ok, but there should be at least a couple of words in English.

Click here to submit your Drupal site!

All new additions are constantly monitored.