Geogebra <--Free software application for geometry, algebra, and calculus

Math Master Mac - Wilson School District CFF Coach Chris McCaffrey's Geogebra Lesson Page - worth a look!

Fooplot <--Online graphic calculator and function plotter
Mathforum <--Collaboration website through Drexel University
Illuminations <--Site created by the NCTM which offers lesson plans and resources
National Library of Virtual Manipulatives <-- Interactive applications for math content areas
Java Gallery of Interactive Geometry <-- Interactive geometry applications
Classrooms for the Future Math Wikispace <--Resources and collaboration opportunities from math teacher in Pennsylvania