Sam Altman: Co-founder OpenAI, broad range of topics more now to do with funding basic research and creating a culture that supports innovation.
Marc Andreessen: Co-founder a16z, this has been inactive for a long time but it is a great source of thoughts on startups and business in general
Alexey Guzey: Researcher on improving philanthropy and science, one of the main inspirations for me starting this blog. Lots of actionable advice to use right away as well as longer posts on life sciences and issues in science.
Patrick Collison: Co-founder of stripe, few actual posts but many excellent lists, the best, in my opinion, and most widely known being /fast for a look at how much progress humans can accomplish on large projects when things go well.
Kevin Simler (Melting asphalt): ex Palantir, very broad set of topics, all excellently written about ranging from beauty to human biases to simulations of contagions.
Nabeel Qureshi: Software engineer at Palantir, not many posts but they are very high quality and touch on a broad range of topics.
Andy Matuschak: One of the most unique blogs around, delving into tools for thought, check out the ‘NOTES’ section.
Devon Zuegel: Product lead GitHub Sponsors, very broad range, lots of great stuff on cities in particular
Kevin Kwok: Formerly at Greylock Partners, lots on loops in business & the person who introduced me to Robert Caro
Julian Lehr: Stripe, Largely technology focused, also one of the best looking blogs of the bunch.
Scott Alexander (Slate Star Codex): Rationalist blog, as of posting this list the blog is currently down but many of his essays can be found online. Especially recommend Meditations on Moloch on coordination problems
Alex Danco: Currently Shopify Money, lots of great essays on a diverse set of topics from philosophy to thermodynamics