We have a topic for each end of the experience spectrum. For those that have done quite a bit with SQL Server:
1. Using the HIERARCHYID data type
What a tree is and the basic rules around trees, what is a hierarchyid, inserting data, retrieving data, changing the tree structure (reparenting and adding new branches)
For those of you getting into it and for those who are about to move companies again here's a great reminder topic:
2. DBA 101 – Figuring out what is THE most important deficiency
You walk into/are handed a completely dysfunctional SQL Server environment, where do you start and how do you fix it without going insane or working 200 hours a week.
It's Mike Hotek so you know there will likely be something relevant no matter what your experience level.