The National Museum of Mathematics:

http://www.mathmidway.org

http://momath.org

NYSED Common Core State Standards for Mathematics

http://www.p12.nysed.gov/ciai/common_core_standards/pdfdocs/ccssi_math_standards.pdf

Source for math teachers: Jefferson Math Project

http://www.jmap.org

College Board:

http://www.collegeboard.org

Math Forum at Drexel College (see the Problem of the Week or Ask Dr. Math):

http://mathforum.org

Summer Math and Science Programs:

http://syosseths.com/documents/Summer%20Science%20&%20Mathematics%20Research%20Programs%202011.pdf

Math for Teachers and Students – lessons and worksheets

http://www.aaamath.com

Mathematical Challenges for the entire family – National Council of Teachers of Mathematics (NCTM):

http://www.figurethis.org/index.html

Games that Instruct – NCTM

http://illuminations.nctm.org