The following are professional websites for mathematics teachers:
AMTNYS Official website for the Association of Mathematics Teachers of New York State

NCTM Official website for the National Council of Teachers of Mathematics

NYSED Official website for the New York State Education Department

The following are NYSUT recommended Math Websites and literature appropriate for K-8:

Illuminations NCTM activities site (K-12)
arcademicskillbuilders.com
aaamath.com
vital.thirteen.org
edweb.tusd.k12.az.us
nlvm.usu.edu
thefutureschannel.com
gamequarium.com
internet4classrooms.com
ctap4.org
mathgoodies.com
learnalberta.ca
pbskids.org
lessonplanspage.com
gaillovely.com

For very young students:
uptoten.com

Math Books:
The Doorbell Rang by Pat Hutchins
The Kings Chessboard by David Birch (exponents)
Two Ways to Count to Ten by Ruby Dee
How Big is a Foot by Rolf Myller
40 Fabulous Math Mysteries Kids Can't Resist (Grades 4-8) by Marcia Miller
If you Made a Million by David Schwartz (http://webtech.kennesaw.edu/reading/ifyoumademillion.htm)
The Hershey's Milk Chocolate Bar Fractions Book by Jerry Pallotta
What's Your Angle, Pythagoras? A Math Adventure by Julie Ellis
Millions to Measure by David Schwartz
Sweet Clara and the Freedom Quilt by Deborah Hopkinson
The Greedy Triangle by Marilyn Burns (http://www.lessonplanspage.com/MathGeoShapesGreedyTriangle14.htm)
Math Doesn’t Suck by Danica McKellar (http://www.mathdoesntsuck.com/)
Shape Up by David Adler
Math Man by Teri Daniels
When a Line Bends….A Shape Begins by Rhonda Gowler Greene
Twelve Snails to One Lizard: A Tale of Mischief and Measurement by Susan Hightower
The Librarian who Measured the Earth by Kathryn Lasky
Venn Can We Be Friends?: And Other Skill-Building Math Activities, Grades 6-7 by Faye Nisonoff Ruopp
The Sticky Problem of Parallelogram Pancakes: And Other Skill-Building Math Act., Gr. 4-5 by Faye Nisonoff Ruopp
The Number Devil: A Mathematical Adventure by Hans Magnus Enzensberger
The Man Who Counted: A Collection of Mathematical Adventures by Malba Tahan
G is for Googol: A Math Alphabet Book by David Schwartz
A Gebra Named Al: A Novel by Wendy Isdell
The Phantom Tollbooth by Norton Juster
Conned Again, Watson! Cautionary Tales of Logic, Math, and Probability by Bruce Colin