LinkedIn (Link)
Edward Frankel's Love and Math
Paul Halmos' I Want to be a Mathematician
Terence Tao's blog
Ravi Vakil's advice to potential PhD students
Ravi Vakil's recommendations of great writings in mathematics
Cedric Villani's Birth of a Theorem
Gappy Paleologo's Buy-Side Quant Job Advice
Gappy Paleologo's The Elements of Quantitative Investing
Headlands Technologies' blog
Hudson River Trading's tech blog
Jane Street's blog
Max Dama's notes on automated trading