List of Interesting Math Blogs I have the one or other interesting Math blog in my feedreader that I follow. It would be interesting to compile a list of Math blogs that are interesting to read, and do not require research-level math skills.
I'll start with my entries:


*

*Division By Zero

*Tanya Khovanova’s Math Blog
 A: Some more that didn't appear in other answers:


*

*Mathbabe

*David Edwards

*Proof Math Is Beautiful

*Into the Continuum

*Low-dimensional topology

*Geometry and the Imagination

*Stochastix

*Sketches of Topology
Additionally, I write isomorphismes which is more about the intersection of maths with humanities than maths per se.
A: Math ∩ Programming. The name is pretty self-explanatory.
A: It isn't quite a blog, but Steven Strogatz's 15 part series for the New York Times was excellent.
A: http://amathew.wordpress.com/
He climbs Mount Bourbaki with the grace of a leaping gazelle. 
A: Not a pure math blog, but it's one of the most fascinating blogs in my RSS. 
Futility Closet
A: Always enjoyed Shtetl-Optimized by Scott Aaronson.
A: Gödel’s Lost Letter and P=NP is a very well written and active blog (also, both in posts as in reactions). Especially for people with an interest in theoretical computer science. 
A: John D Cook writes The Endeavor
One of the MathWorks blogs: Loren on the Art of Matlab
... a few more:
eon
Peter Cameron's Blog
Walking Randomly
Todd and Vishal's Blog
(Check their blogrolls for more)
A: Although it's still new, I hope that my blog is pretty interesting. It details some of my recent research, things I currently am looking into, and some recreational math along the way. (I also use it as a teaching supplement to my students, but I bet that won't be too interesting here).
A: Not always pure math, but I think John Baez' This Week in Mathematical Physics contains a lot of really interesting math reads.
I should add Terry Tao's What's new. It's a very active math blog (both in posts and comments) and definitely covers some cutting edge math, even if it can be way over my head.
A: Timothy Gowers' blog is excellent.  Like Terence Tao, he is both a Fields medalist and an excellent writer.  Together their blogs were my first real introduction into how professional mathematicians think, and their writing has taught me a lot, both about mathematics and about mathematical writing.  If you are a serious student of mathematics you will find all the blogs you need by scrolling through their blogrolls.
A: Cedric Villani's news is relatively new and looks quite interesting (even when messed with by google translate).
A: For statistics and related topics, see the very interesting:
http://andrewgelman.com/
See his blogroll for more of the same!
A: Here is an entire list of math blogs.
A: Wild about Math! and SatMathBlog (more for amateurs)
A: For those who are teaching in high school or what not: gaussianmath
A: If your interests extend to game theory and mathematical economics look at here  and   here.
A: For those of you that can speak french, there is the wonderful http://images.math.cnrs.fr/.
It is aimed at a wide public, but all articles are written by researchers and most are fascinating!
A: I find Annoying Precision to be wonderfully readable, and has many many interesting topics. Additionally, Rigorous Trivialities is a bit higher level, but has a really useful intro to Algebraic Geometry.
A: Gil Kalai's blog is pretty awesome. Mostly covers combinatorics.
A: Secret Blogging Seminar
A: Math-blog is one I have in my google reader and I just found this one through google reader but it's a little over my head:The Unapologetic Mathematician
