I know Good Math, Bad Math. And of course there’s this blog. And there are many other small math blogs – Integrating the Derivative, Polymath, Halfway There, ChapterZero, Exponential Curve, Kitchen Table Math, and Casting Out Nines, to name a few. I’m not sure if Not Even Wrong is a math blog or a physics blog.
But I don’t know of any really big math blogs except Good Math, Bad Math. If anyone knows any, please do tell me about them… I’m always looking for good mathematical conversations.