11011110 David Eppstein, graph theory.
360 Two mathematicians whose blog reminds me of Martin Gardner.
dy/dan Edgy, introspective, fearless.
JD2718 Deep mathematics, and tidbits about the politics of education in New York.
Math Stories Mr. K, middle school math.
Math Teacher Mambo 12th grade teacher in Texas.
Mathematics Education Research Handy addition for the reader: every link to every math ed article that gets released.
The Math Less Traveled Clear exposition of higher mathematics.
MathNotations Contests and puzzles aplenty based on regular high school algebra.
Mathpuzzle A repository of nearly everything in recreational mathematics.
Terry Tao Possibly the best mathematician in the world.
Timothy Gowers Thoughtful writing about higher mathematics from a Fields medalist.
The Numbers Guy Stats columnist for the Wall Street Journal.
XOR’s Hammer Set theory and logic.
Annoying Precision Sophisticated thinking about higher mathematics.
Continuities Jackie Ballarini, teacher in Chicago.
Division by Zero Dave Richeson; college level mathematics, but one of the clearest writers out there.
f(t) Kate Nowak: teacher, introspector extrodinaire.
Gödel’s Lost Letter and P=NP Extremely fine writing about issues in computer science and related mathematics; possibly my favorite blog.
neverendingbooks Quirky writing mostly about noncommutative geometry, group theory and math history.
Rip’s Applied Mathematics Blog Lengthly writings about the author’s personal projects.