There are numerous Mathematics blogs out there!
Use Mathblogging.org to see recent posts from an extensive collection of blogs. Note the various categories including Teachers.
For Weekly Picks click here.
The Edublogs Directory has a Math and Science Section, like Mathsblogging.org it is possible to see when each blog was last updated.
A site always popular with my students who like the very clear notes available is mr barton maths.com. Mr Barton also has a blog , note the link to the lovely set of 30 puzzles in his recent post - Lovely Puzzles.
Craig Barton has included some of his own favourite blogs in this video (thank you for the mention Craig!):
A blog I have mentioned previously is ‘Teaching AQA GCSE Maths’ from the Longman Maths publishing team. Obviously this is of particular interest to teachers teaching the AQA specification, however they sometime provide free resources of interest to any Maths teacher. This recent post for example features a free algebra resource including teachers’ notes. This works very well on the interactive whiteboard. An earlier post gave a link to a free book – ‘Street Fighting Mathematics’ by Sanjoy Mahajan. The post includes a link for a free pdf download. This page of their blog has links to many free resources. Thank you Longman Maths!
Some of the Nrich team can be found on Twitter and also have blogs. See the note at the foot of Jennifer Piggott’s article.
Some more of my own favourites include Dan Meyer’s blog, Number Loving from Sharon Derbyshire and Laura Rees-Hughes, Great Maths Teaching Ideas from William Emeny and Guillermo Bautista’s very well organised ‘Mathematics and Multimedia‘; this includes an extensive collection of clear tutorials on GeoGebra. For further links on Geogebra see this earlier post.
On the subject of blogging itself see Blogineering from Guillermo Bautista and Riley Ayes. The very busy Guillermo also has a blog ‘Mathematical Palette‘ where he discusses the connection between mathematics and other fields such as the arts, music, poetry, and other sciences. My favourite post to date has to be Mathematics and Hairdressing!

The blog you are reading now is a WordPress blog – see my very first post for some useful links on learning to use WordPress. See also this link for some useful information on using Blogs with students.
Hi Colleen. Thank you very much for mentioning Math Palette.
My pleasure Guillermo. I intend doing a new post on reading soon as well.
I am thrilled that you attribute your start up to me – I think you’d have done it anyway – but thank you!
Hi Colleen! Thank you for recommending us, as you know it is your blog that inspired us to start up!