Math Mania

I am serving on a math teacher's focus group for my county with the idea of helping to incorporate technology into the lessons.  My hope is that Smart and Promethean files will be created and disbursed to teachers for use, but I would also like to generate a list of helpful free websites that teachers can you for demonstration purposes as well as for student individual practices.  I will include some I have used in the past.  Please add sites you have found successful with your students or children!

• Create a Graph--I found this site very useful in data units with students.  Students could even create a survey using Survey monkey and then use this website to create graphs of the data they collect!
• Harvey's Homepage--I have had the pleasure of seeing Harvey at two different conferences.  His Smart resources are amazing and really engage students!
• BBC BiteSize--I LOVE  BBC's resources they have a site for younger students and for older students.  Check out their activities for other content area also.
• Arcademics--I got introduced to this site at ISTE this past summer, and have used it throughout the year.  The games really engage the students in their math facts.
• WolframAlpha--this search engine helps you solve math problems and gives you explanations as to how and why the answer is correct.  This could be an excellent tool for older students. 

And at this point i realize I have been neglecting my Diigo account, as I know I have oodles other sites bookmarked on my work computer.  What are some of your favorite (and free) math sites to help students review or reinforce new skills?