AAAMath - A comprehensive set of interactive math lessons, covering all topics for grades K-8.
BrainNook - A free virtual world for kids to practice their Math and English skills. Accounts do not require registration, but by registering, you access premium features including reports of kids' activity.
Brightstorm - Over 2,000 free help videos covering Algebra I to Calculus, including math homework checker. Also available are SAT, ACT, PSAT and AP Test Prep programs for pay.
Fuel the Brain - Free resources for K-3, including printables, games and interactives.
F.R.E.E. (Federal Resources for Educational Excellence) - Learning resources from federal agencies including animations, photos, and videos on topics such as Algebra, Geometry, Data Analysis, Measurements, etc.
Game Classroom - Free and fun interactive math games.
GeoGebra - A free, dynamic mathematics software package for download with interactive graphics that joins geometry, algebra, tables, graphing, statistics and calculus.
Hip2B2 - A unique initiative that aims to spur curiosity in science and math in everyday life by showing learners that these subjects can be loads of fun while being important to their future success.
Illuminations - Activities and lessons designed to enhance the teaching and learning of mathematics. Sponsored by the NCTM. K-12.
Interactivate - Almost 300 interactive Math activities, great for use on the SmartBoard.
Khan Academy - An extensive collection of videos, covering all math topics from K-12. Also includes practice exercises, assessments, tracking of skills, and badges for completion of exercises.
Manga High - A free, game-based, K-12 math teaching resource. Teachers direct and control the math learning experience for the kids. Students are assigned a log-in and password. Teachers manage their class and set challenges and activities on a class-level or student-level.
Math Apprentice - A site designed to reveal the connections between math and real-life by showing how math is used in a variety of professions.
Math Live - Presented in an engaging television show format, Math Live teaches math concepts through 23 animated lessons. During the lesson, students use interactive tools to demonstrate their understanding of the lesson. Each lesson is also accompanied by an assessment worksheet.
Math Moves U - An innovative site designed to engage students through interactive learning programs like contests, events, scholarships, tutoring programs and more, designed to capture the imaginations of students, fueling their interest in math by providing rich content tied to their passions.
MathNook - Free, online flash games to practice math skills. Also includes other teaching resources, like a worksheet generator and pre-made worksheets.
Math Open Reference Project - A free, interactive math textbook, initially covering US Geometry, that uses animations and interactive tools to teach math concepts in fun and engaging manner.
Math Pickle - Professional development videos of math problems along with supplemental presentations and hand-outs.
Math Playground - An action-packed site for elementary and middle school students to practice math skills, play games and have fun!
Math Snacks - Educational animations, mini-games and interactive tools to help learners better understand math concepts. The "snacks" are designed to present mathematics in a very different way.
Math Train - Compilation of math instruction videos, both student- and teacher-created. Podcasts also available on iTunes.
National Library of Virtual Manipulatives - A library of interactive, virtual manipulatives to help students visualize relationships and applications.
NSDL (National Science Digital Library) - A national network of digital environments dedicated to advancing science, technology, engineering, and mathematics teaching and learning, including high quality, interactive resources that help educators bring cutting-edge, real-world science and math into their classrooms and stimulate excitement for science in today's digital learners, web-based applications that help teachers and learners to optimize their experiences with digital content, and more.
StudyJams! - Animated videos and lessons, complete with tutorials and quizzes.
That Quiz - An online assessment tool, especially useful for math practice and testing. Students do not have to register to take the quizzes, and teachers who register have access to more test-generation tools.
Wolfram MathWorld - Toted as "the web's most extensive math resource", MathWorld is a free service that provides almost 13,000 entries that are extensively referenced in journals and books spanning all educational levels, including those read by researchers, elementary school students and teachers, engineers, and hobbyists.
XtraMath - A free, web-based, math facts fluency program, dedicated to math fluency for all!
Yummy Math - A great site to provide teachers an easy-way to bring real-life math problems and scenarios into the classroom.