I'm making this post partly prompted by someone who asked me and other fans of Scott's to recommend some favourite posts from the archives for new readers, and partly because I'm planning a post based on some of his most recent posts, so I wanted to write this as context in case people don't know who he is when I mention him.
I found the "recommend your favourite post" request hard, as I have trouble consciously remembering specific essays of Scott's and what's in them, but I do find his ideas have shaped my thinking so much that I sometimes say or write things I think are my own ideas and later embarrassingly find them in one of his old essays, where I must have first come across them. But here's a non-exhaustive list of some of his posts I particularly like.
https://slatestarcodex.com/2014/09/10/society-is-fixed-biology-is-mutable/ contrasts social and biological solutions to social problems, e.g. banning leaded petrol; https://slatestarcodex.com/2015/01/31/the-parable-of-the-talents/ is about innate ability versus effort, and uses the straightforward example of basketball ability to illuminate the emotionally and politically fraught example of intelligence; https://slatestarcodex.com/2014/09/30/i-can-tolerate-anything-except-the-outgroup/ is about the paradox of tolerance and about the outgroup not necessarily being who you think it is; https://slatestarcodex.com/2014/11/21/the-categories-were-made-for-man-not-man-for-the-categories/ explores where you draw the lines between categories and why, because often there's no factually correct division but just a variety of possible divisions with different tradeoffs; he argues convincingly in favour of accepting trans people as the gender they say they are, which makes it a good one to cite against the people who bafflingly label a Jewish Democrat-voting Trump-denouncing blogger who lives in a poly group home in California as a dangerous right-wing extremist; and https://slatestarcodex.com/2014/11/03/all-in-all-another-brick-in-the-motte/ popularised the concept of a motte-and-bailey argument, a discussion about which was what prompted the original request for post recommendations.
https://slatestarcodex.com/2014/03/17/what-universal-human-experiences-are-you-missing-without-realizing-it/ covers things like aphantasia (lack of visual imagination), and I just find the general principle of the essay really useful and insightful: to remember not to assume your own experiences are universal. https://slatestarcodex.com/2017/10/02/different-worlds/ is more of the same (i.e. people's experiences are more different than you realise), but on an interpersonal rather than individual sensory/mental level. It deals with filter bubbles and the way that people, presumably through no fault or merit of their own, just seem to consistently find themselves surrounded by certain types of people and thus have certain types of life experiences which are dramatically different to those of other seemingly-similar people. I am not the woman quoted in part IV, but I could have written something similar.
https://slatestarcodex.com/2018/01/24/conflict-vs-mistake/ categorises two different approaches to disagreements; the first couple of paragraphs are a bit jargony so I recommend starting with "Mistake theorists treat politics..." When I first read this, I thought it was saying that mistake theory was obviously right and I thought its description of conflict theory was a grotesque caricature of how some other people allegedly operate; and yet there are people who read it and came away identifying as conflict theorists, so again that shows how people are more different than I first believed.
https://slatestarcodex.com/2014/03/08/the-slate-star-codex-political-spectrum-quiz/ captures a distinction in political attitudes that's quite central to my thinking and a concept I often want to refer people to.
He's also doing some really interesting original research on birth order effects (see https://slatestarcodex.com/2018/01/08/fight-me-psychologists-birth-order-effects-exist-and-are-very-strong/ ). His annual survey of around 8000 people who read his blog skews heavily in favour of firstborns, and he's controlled for things like "some demographics have larger families so are less likely to be firstborns): just out of readers with one sibling, 71.4% of them are the elder. An interesting question is what exactly is being correlated with firstborn-ness here. It's something like intelligence, but not precisely that: the effect doesn't seem to be as strong in groups that are selected for intelligence but not selected for a kind of nerdiness or intellectual interestedness. People have suggested all sorts of armchair theories about why the correlation might exist, some biological (e.g. parental age, depletion of maternal nutrients) and some social (either that firstborns get more parental attention because there's less competition, or that later-borns have the advantage of a close-age peer to copy from and interact with, whereas firstborns have to learn to figure out more stuff for themselves and/or spend more time in their own imagination), so Scott is working on refining his results by drilling down into the effects of biological versus social siblings (e.g. biological siblings you didn't necessarily grow up with, versus adopted or step-siblings that you grew up with but weren't biologically related to), and I'm looking forward to seeing those results.
There was a post on his old LiveJournal on futarchy (which I can't now find on archive.org), which was the first one I remember ever reading and thinking this guy is worth following.
I also love his short stories, especially https://slatestarcodex.com/2018/10/30/sort-by-controversial/ , which is a really insightful take on social conflict in the internet age, and has given us the concept of a "scissor statement", which is a generically useful piece of mental architecture in the same way as "motte and bailey"; https://www.gwern.net/docs/fiction/2011-yvain-thestoryofemilyandcontrol.html , about an identical twin who is the "control group" for her sister, which is chilling and creepy and a great example of interesting speculative fiction; and https://slatestarcodex.com/2015/06/02/and-i-show-you-how-deep-the-rabbit-hole-goes/ , which is just really fun.
He also makes some very fun, silly, and nerdy posts, like the recent https://astralcodexten.substack.com/p/list-of-fictional-cryptocurrencies , or his collections of Swifties, which are the best and cleverest I've seen anywhere: https://slatestarcodex.com/2014/08/14/fifty-swifties/ https://slatestarcodex.com/2015/06/15/fifty-more-swifties/ https://slatestarcodex.com/2015/10/02/swifties-3-the-race-is-not-to-the-swifty/