According to Dr. Mel Levine in his book A Mind at a Time,

"Parents should be responsible for the ongoing automatization of skills and facts. There should be drill on math facts, letter formation, basic vocabulary, or spelling each night at bedtime (the best hour in which to consolidate new information in long-term memory). School affords virtually no time to achieve automatization and in instances where kids have problems with automatic memory, parental assistance can be the only thing to prevent a student from acquiring that dangerous and disheartening feeling that he is too far behind to catch up."

A Mind at a Time (2002) by Mel Levine, M.D. (Founder of All Kinds of Minds Institute - http://www.allkindsofminds.org - and Director, Center for Development and Learning

AplusMath
www.aplusmath.com

Arithmattack
http://www.dep.anl.gov/aattack.htm

Elementary Interactive Math Web Sites
http://edweb.tusd.k12.az.us/ekowalcz/math/elementary_web_sites.htm

Web Math
http://webmath.com

Math Forum
http://mathforum.org/

Math Games
http://www.funbrain.com/cgi-bin/getskill_s.cgi?A1=selects&A2=math&A4=0&A7=0

Math Web Resources
http://www.ct4me.net/math_resources.htm

Elementary Mathematics
http://www.internet4classrooms.com/math_elem.htm

Educational Java Programs (math)
http://arcytech.org/java/

Webmath
http://www.webmath.com/

National Library of Virtual Manipulatives
http://nlvm.usu.edu/en/nav/index.html

MathVIDS
http://coe.jmu.edu/mathvidsr/default.htm

Mathplayground
http://www.mathplayground.com/flashcards.html