I know there are (or at least should be) a default configurations at
/etc/i3/config.keycodes. But it is rather basic, intentionally so. It is designed to get one started but it does not showcase half of what i3 is actually capable of.
There is the - IMHO excellent - User's Guide that lists and explains every single command and configuration option.
And of course, there is this FAQ site that provides answers to a lot of questions, often in the form of configuration snippets.
But sometimes just knowing the parts is not enough: You may know what the parts do, you'll be able to build something, it probably will even work. But it takes time and experience to get something that works as well.
So, this question is essentially a request to share (post and/or link to) your configuration - or maybe even configurations of others you found useful. So that beginners have a starting point and experienced users a source of inspiration. There may be a lot of i3 configurations available around the Internet, but this site is the only one that is actually linked from the offical i3 website.