Ask Lemmy

Baseball - its' history, I can go off on teams and players from a century ago.

Music - rock of nearly all genres, electronic, soul, jazz, blues, some classical and contemporary.

Cinema - I used to screen films for a local cultural center, everything from gritty psychedelic British crime thrillers like Performance to French new wave gems like Pickpocket, from classic Hindu cinema like Pather Panchali to twisted Japanese horror like Suicide Club, and anything in between.

Cosmology and Physics - a lifelong passion, I have some astronomer friends (there's an institute in my city) and can hold my own in conversation with them. Lately I've been getting a handle on things like Lorentz Transformations and Bell's Inequality Experiment (aka Quantum Entanglement).

Painting - the history of the medium, and although I prefer Modern Art, starting in the mid-19th century onwards, I can now navigate and appreciate the styles that have appeared through the centuries, say the differences between Renaissance, Baroque and Rococo.

EDIT: How did I forget Science Fiction?
I've read all of Isaac Asimov's stories on Foundation and the Galactic Empire, including some of the more obscure ones like "The Stars, Like Dust", "The Currents Of Space" and "Pebble In The Sky". Also, many of his standalone stories, such as "Nightfall" and "The Gods Themselves".
Hands down, Asimov is my favorite Sci Fi author, and I love the original "Foundation" trilogy like no other.

The first four books of Frank Herbert's "Dune" saga.
A whole bunch of Harlan Ellison's short stories.
Several of Philip K Dick's novels.
Throw some JG Ballard and William Gibson in there, for good measure.