CAS is considered one of the authors of the canon, despite not being explicitly named in Gygax's Appendix N, as he wrote for many of the same publications as, and was a close friend of Lovecraft.
I've linked items I've been inspired to write up from his work below. I expect more will be added later. Obviously, I find quite a few ideas in these stories, yet they're not an easy read. He's one of the few authors who makes me reach for a dictionary - the last one was John Marshall in his The Life of George Washington - because of his extensive and anachronistic vocabulary.
I was tempted to recommend you find a more cohesive work, say his Averoigne stories, but then I realized how much of the inspiration is coming from the other genres he worked in.
[Ed. Forgot to put in the links!]
Goddess of the Ebon Moon
Portal of Eibon