I've collected all the ingredients for all the archived IRON DM tournaments in spreadsheet and broke them up into 7 categories
Places, Monsters/Animals, People, Objects, Events, Abstractions and Other
"Other" is where things that I could not quite codify, or that could be obviously interpreted in more than one way as to fit in more than one category. An example is "Autumn" - which you can call an "event" but it s kind of a long and nebulosu time-period marked by weather changes that could be used in a number of ways in an entry.
If any one can think of a better way to break them up - please let me know. I'll attach the spread sheet here.
I hope to add them to the site soon, and also have a separate list of "descriptors" that were used for many of the ingredients.
Among the patterns I could see variations of harpies, monks, ghosts and zombies are all popular as ingredients, and "Betrayal", "Hangman's Tree" and "Rod of Wonder" were bother used more than once - as were things with the "shadow" descriptor.