See these previous questions:
http://www.question2answer.org/qa/43/are-there-any-other-sites-that-run-the-software
http://www.question2answer.org/qa/645/is-there-a-big-website-using-q2a
http://www.question2answer.org/qa/370/are-you-using-q2a
Besides the links mentioned by DisgruntledGoat you as well can have a look to the users site, some of them have listed their site next to their account information. However, a showcase as well would be a great idea.
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask here, in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.
