See Appendix C in our Van de Walle textbook then click here for the blackline masters or here for textbook resources.
Area
and Perimeter Applet from http://www.mste.uiuc.edu/java/
Virtual Geoboard (plain one) from http://matti.usu.edu/nlvm/nav/vlibrary.html
*Virtual Geoboard (with coordinate axes) from http://matti.usu.edu/nlvm/nav/vlibrary.html
Draw lines of symmetry from E-labs.
Reflection, Translation, and Rotation Tool from E-labs.
*Combining Transformations (it's a game!) from E-labs.
*Reflection, Translation, and Rotation Tool from NCTM
*Tessellate a Triangle movie - from Mike Shepperd
*Tessellate a Quadrilateral movie - from Mike Shepperd
Tessellate a Quadrilateral from Shodor.
Tessellate a Quadrilateral from psu.
Rotations "Around Midpoints" of Triangles from Totally Tessellated
Geometric Solids from NCTM (Note: shift-click to color faces and edges).
Virtual Pattern Blocks from arcytech.
For more see my Teaching Resources.