I just found a new subreddit for sharing Docker files: http://www.reddit.com/r/Dockerfiles/
This is pretty neat, since a few Google searches didn't yield any other good communities where Docker files are being shared and aggregated on a forum, other than a basic GitHub search.
The subreddit is less than one day old, and it has 8 posts at the time of this post's publication. It was created by Russell Smith and I hope it, or something like it, really takes off. I think it's going to really drive the developer community forward when Docker matures rapidly within the open source community.