Interactive Area Explorer - Fix the perimeter, and then find the area
http://www.shodor.org/interactivate/activities/AreaExplorer/

Interactive Perimeter Explorer - Fix the area, and then find the perimeter.
http://www.shodor.org/interactivate/activities/PerimeterExplorer/

Interactive Perimeter and Area Explorer - Find both the perimeter and the area of the shape.
http://www.shodor.org/interactivate/activities/ShapeExplorer/

The shapes include compound shapes.

http://www.bgfl.org/bgfl/custom/resources_ftp/client_ftp/ks2/maths/perim...

Drag the pieces into the factory and build three spaceships.

http://pbskids.org/cyberchase/games/perimeterarea/perimeterarea.html

Choose to solve problems on perimeter of a rectangle, area of a rectangle or both perimeter and area of a rectangle.

http://www.funbrain.com/poly/index.html

This resource attempts to emulate a cell phone calculator. The teacher can demonstrate how to use the simple calculators to do useful real world maths. At the moment 2 types of real world questions can be generated by the resource: percentage discounts and area.

Instructions
http://www.teacherled.com/2009/01/03/cell-phone-maths/

Resource
http://www.teacherled.com/resources/cellphone/cellphoneload.html

Students have to choose the correct operation to solve each problem, which can involve radius, diameter, circumference and area.

Students can also do an investigation to discover that for any circle, circumference divided by diameter is always about 3.14. Neat activity!

http://illuminations.nctm.org/ActivityDetail.aspx?ID=116

Changing the Border
This is a nifty puzzle whose solution is based on the area of a triangle. The land is divided into two parts (P and Q) by the border ABC. Redraw a straight border line passing through point A so that each of the areas does not change.
http://www.ies.co.jp/math/java/geo/tochia/tochia.html

Dividing a Quadrilateral
This is a more challenging problem that is based on the same underlying concept.
http://www.ies.co.jp/math/java/geo/shi2to/shi2to.html

Practice estimation skills by determining the number of objects, the length of a line, or the area of a shape. Choose the problem type, or choose 'Random' to see a mixture of all three types of estimation questions.

http://www.shodor.org/interactivate/activities/Estimator/

Tangrams are a versatile manipulative. They can be used to build understanding of geometry, fractions, area and other topics. This is a Java implementation of tangrams.
http://nlvm.usu.edu/en/nav/frames_asid_268_g_1_t_3.html?open=activities&...