From site:  MathTV.com was created in 2000 as a way to help students struggling with math to easily and quickly learn the concepts needed to succeed. Our math video lessons offer students an alternative learning experience outside the classroom without the high cost of personal tutors.

Whether you’re in need of homework help or some additional resources for test preparation, our videos and worksheets can be a significant learning asset. Watch and learn as our math instructor clearly explains the steps and concepts involved in solving even the most advanced equations.

This is an online interactive dictionary of math terms for math topics.  It has animated definitions, examples, activities and a calculator. Also available as an iPhone/iPad app called Maths Charts.

Note that this dictionary uses Australian English spelling so some words will be spelling a little differently from American English (maths for math, colour for color, metre for meter). Jenny Eather provides charters, posters, and classroom displays for teachers.

From site: 

Welcome to Math Playground, an action-packed site for elementary and middle school students. Practice your math skills, play a logic game and have some fun!

Math Playground was created by teachers who are passionionate about math and technology. Many of the activities on the site were inspired by the hundreds of students we have had the pleasure to teach over the years. Other activities have been provided by generous educators and programmers who share our passion for making learning fun. Math Playground is not affiliated with any school, business, or organization.

Mathematics Glossary  is a free interactive math reference tool for students of all ages.  It’s also useful and a refresher for parents and teachers.  You find the math term, such as addend or histogram, using their alphabetic index.  Or you can look at a list of relevant terms by grade level.  The site provides a definition of the math term, graphic examples, and, in some case, real life examples. 

This glossary is still a work in progress.  Terms used up to grade 6 are complete, but less than half are accessible for the higher grade levels.

This site provides interactive math exercises and problems.  They include a series of basic math lessons for introduction and review. as well as practice problems for some lessons.