Aspies sure love to make lists, don't they? I think that trait may be as common as, say, not making eye contact, gullibility, or poor social habits. Anyway, here's a little of what I'm into.
Torture devices throughout the ages and from different cultures.
Methods of execution throughout the ages and from different cultures.
Obscure Romantic composers (I collect symphonic music and solo piano music from the Romantic era).
Researching varieties and species of plants and animals. For instance, learning about all the different types of tomatoes, zebras, wildebeests, mushrooms, peppers, monkeys, mangoes, coconuts, corn, etc.
Making lists of the uses of the most versatile fruit or vegetable. (So far I'm leaning towards the tomato although Native Americans would beg to differ and claim it's corn because, so far, they have 32 uses for it).
The psychologies behind why certain groups of people follow one particular dictator/king/chief/khan/etc.
The NYC Subway map.
Is being a "completionist" unusual. By that I mean, for instance, I don't simply have a few albums of music from, say, Franz Liszt - I have his complete non-vocal works - 106 albums. For Mozart, it's 74. For Beethoven, it's 42, etc. I also collect discographies and bootlegs of groups I like - KISS, Iron Maiden (48 albums), Judas Priest (48 albums), Rush (36 albums), Slayer, Anthrax, Megadeth, Metallica (30 albums), many others.