Free Math Websites for Grades 6-12

Do you have a favorite website that is your go-to for math ideas? Here are my top 9 favorite free math websites I use in the classroom.

Graphing:
geogebra.org: This website takes a little getting used to, but is great once you get the hang of it! Create your own dynamic activities or use one that's been shared online.
​desmos.com: Consider this the new generation of graphing calculators.

Tutorials:
katesmathlessons.com: Check out the math lessons, practice problems, and videos I've created to help my own algebra and geometry students.
purplemath.com: Lots of great tutorials here (geared towards older students)
coolmath.com: Middle School and Elementary lessons 

Blogs:
There are tons of of excellent math blogs out there you should make sure you're reading! My favorites are dy/dan, f(t), and yummy math.


Why did I pick 9 instead of 10?  My 10th favorite website isn't totally free, so I didn't think it was fair to have it in the official list.  I also love using IXL in the classroom.  I have a classroom account and love that it gives students instant feedback when they get a question wrong. 

How about you? Do you have any favorites I should add to the list?