In no particular chronological order...
--reptiles (especially constricting snakes)
--classical music
--guitar (a constant-It's been the #1 interest my whole life)
--Politics
--Astronomy
Looking at the list I notice that some of them I don't have nearly the interest I did, while others (specifically the guitar and classical music) are just as intense as always. It's strange, because when I was into snakes I was totally into them--I had many terrariums, I bred my own food, and I could have probably charged admission to my room to look at the pythons, boas, and monitors. Now I don't really care.
Astronomy is a recent one, I've always been interested, but I've taken some classes, and now I'm getting that familiar feeling. I'm buying optical equipment, taking trips to observatories, and generally going overboard once again...
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O Wonder! How many goodly creatures there are here! How beauteous mankind is!