The Thirty-Six Dramatic Situations (edition 1977)

Here it seems that Polti just started listing plots until he got to 36. I do recommend this book, along with Games People Play by Eric Berne (which falls under the psychology/self help section) as a good resource for when you're stuck for an idea. Eric Berne was a psychologist, concerned with figuring out what the basic transactions between people are (games) and what are reasons are for playing them. The difference here is that Eric Berne acknowledges that his list is a work in progress, and more games will be recognized as time goes on.