Killer Tomatoes or their equivalent. (Not that there's anything wrong with loving B-films. Killer Tomatoes have their place.)
I sometimes like to think of sci-fi books as food, since they are, in essence, food for the brain (or food for thought, if you will). Things like comic books and Star Trek novelettes and quirky/kitchy anthologies organized around a central hokey theme are fun. They are the pop tarts and candy bars of the sci-fi world. My unrefined brain-palate could graze on these all day and never tire (It's true. There have definitely been days I have spent in bed or on park benches just devouring this stuff.)
But my problem is that I have super-smart friends. The kind of friends with discriminating tastes. They only consume the pineapple-glazed seitan cutlets and brussels sprouts of science fiction. They know their Assimov from their Bova, and have memorized passages of Ursula Le Guin just because they liked the way the words fit together to describe a concept. Every now and then we chat Lovecraft (for he's one of the rare writers who is both pop tart and brussels sprout), but by and large I embarass them with my geeky love for sci fi with questionable literary merit.
And when the embarassment gets to be too bad, I am punished with a brussels sprouts assignmnet. I promised a friend I would read any book they thought I really couldn't afford to be without.
My friend chose Robert Heinlein's 1966 novel The Moon is a Harsh Mistress. And I did it. While I can tear through several books of pop tart sci-fi in a day if left to my own devices, this book took me two weeks to complete. It's a hard book. The people of the lunar colony Heinlein writes about have their own Loony language, who use it in unique ways, kind of like how the characters in A Clockwork Orange did. This, plus the super-detailed and slow-moving plot meant that my brain had to engage with this sci-fi in a whole new way.
But you know what? Like brussels sprouts, it was good for me. The slow pace allowed me the time to digest the complications in plot and character, and to think about the core tenets of sci-fi. By the time I finished the book, I had a new found appreciation for the grandfathers of the genre. They are the ones who created the tropes and set the parameters and showed writers that we could demand more from their works, and readers that we could demand more from the work of others.
Having read Heinlein, I feel that I have a better understanding of how the genre has developed throughout history, and I think this will make me a better sci-fi writer. Just like how modern philosophers have to start off with The Allegory of the Cave, so do modern sci-fi writers have to pay their dues and understand how it began in order to take it into new and uncharted territory.