SF Signal has the following post. Thought it was pretty cool:
18 Non-Fiction Essays by Science Fiction and Fantasy Writers
Amazon has had these non-fiction essays available for a while now, but these 18 shorts just popped up in feeds. I didn't realize there were so many, and there are probably more...but for now, here's a list of 18 of them with their descriptions. They are available in full for fifty cents each from Amazon.