The class blog 3010tangents was a class blog for Math 3010, taught by Dr. Evelyn Lamb at the University of Utah. Posts were tangentially related to information information encountered in class, hence the name. Tangent also has a mathematical meaning as well, of course. (html)
The writing on the blog is quite good, and consists of researched pieces on various elements of mathematics.
It’s interesting to me that this site has the same issue as class wiki. These are great treatments of various subjects, but they are subject to decay, they can’t be built on or out.
For a more bloggy approach to mathematical blogging, see Blogging the Foundations of Math