@codinghorror and @Dax at meta.discourse.org provided me with excellent resources and suggestions on where to find even more that I browsed through. Here is a summary.
New user guide
A guide for moderators
Useful topics for staff
- How to use category security settings to control access to content
- How do I create a whisper post?
- How to create Polls
- How to create a Timed Topic
- What is a Wiki Post?
- What are Topic Templates?
- What are Badges
- What are Flags and how do they work?
- Description of various user states in Discourse
- What is the difference between Closed, Unlisted and Archived topics?
- Discourse vs email and mailing lists
More guides are available in the #howto category. I linked it sorted by views as well to help you find the most useful ones.