Okay, if you’re hunting for what typically shows up on a ‘Top 100’ sci-fi books list, let me paint a broad, friendly map rather than a rigid scoreboard. Different publications and communities tilt in different directions—some favor classics, others push contemporary waves—but there’s a core of books that almost always pop up. Expect canonical pillars like 'Dune', 'Foundation', 'Neuromancer', '1984', 'Brave New World', 'The Left Hand of Darkness', and 'The Hitchhiker's Guide to the Galaxy'. Classics mix with later breakthroughs such as 'Snow Crash', 'The Three-Body Problem', 'The Road', 'The Forever War', and 'Hyperion'.
Beyond those, most lists sprinkle in social-dystopia and near-future gems: 'Fahrenheit 451', 'The Handmaid's Tale', 'The Power', 'The Windup Girl', and 'The Man in the High Castle'. Hard-SF and space opera favorites often include 'Ringworld', 'The Moon Is a Harsh Mistress', 'Red Mars', 'Leviathan Wakes' (the first 'Expanse' book), and 'Contact'. For mind-bending, you’ll see 'Solaris', 'Permutation City', 'The Stars My Destination', and 'A Canticle for Leibowitz'.
If a full, numbered top-100 is what you want, check large-community polls or critics' lists—Goodreads crowd lists, magazine roundups, and awards-survey compilations tend to be where the complete enumerations live. My two cents: whether you chase a numbered list or assemble your own, mix eras and subgenres; the joy of sci-fi is how elastic it is—there's always something that surprises you when you least expect it.