Khan Academy - Videos on everything from Arithmetic to Calculus
National Library of Virtual Manipulatives - Games, Spinners, and other Interactive Manipulatives to use on a Smart/Polyvision Board
IXL - Online Math Practice
NJCTL - NJ Model Curriculum based Smartboard lessons and pacing guides.
Xtramath - Free online practice to increase addition, subtraction, multiplication, and division skills/speed.  Can be used as a math center.
Smart Exchange - A collection of downloadable pre-made Smart Board Lessons.  Create a free account and browse by standards, grade, and subject. - various technology based resources for classroom use.  Random name pickers, Fake Facebook pages/text messages, and more.
Drexel University Math Forum - Ask Dr. Math, Problems of the Week, Puzzles, Tips and Tricks.
Math Warehouse - High School Level Math resources.  Algebra, Geometry, and Trigonometry.
NYC Tasks, Units, and Student Work - Common Core based questions, lessons, and units posted by the NYC DOE.