National Council of Teachers of Mathematics
The Math Forum: Suzanne's Mathematics Lessons 2001
This site by Suzanne Alejandre offers lesson plans, activities and resources covering topics in algebra, geometry, data analysis, number & operations, and measurement. The contents of this site are aligned with the NCTM standards and...
National Council of Teachers of Mathematics
Nctm: The Math Forum
This is a useful site with lesson plans, problems of the month, etc.
Other
Tufts University: Early Algebra, Early Arithmetic
This online resource is from the Tufts University offers lesson plans, worksheets, and ideas about using algebra with elementary grade levels.
PBS
Pbs Teachers: Building Boxes [Pdf]
By determining the dimensions necessary for building a box with the greatest volume, students will explore the world of polynomial and rational expressions. Graphing calculators can be used for this activity.
Purple Math
Purplemath: Lessons and Tutoring: Reviews
An algebra teacher's treasure from Purplemath.com. This collection contains links to over 20 links for algebra lesson plans and other resources.