A matching game for number facts, decimal and fraction conversions, and measurement conversions.
http://www.mathsframe.co.uk/cardgame.swf

Other resources by this author can be found at:
http://www.mathsframe.co.uk/free_resources.asp

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

Choose centimetres or inches, and then a level (Easy, Medium, Hard or Super Brain).

http://www.funbrain.com/measure/

Measure the length of the parcel in centimetres, find its mass and decide which size stamp to put on it to mail it.

http://www.bbc.co.uk/schools/ks2bitesize/maths/activities/measures_fs.sh...

Click on the link below to download this flash activity, where students are asked to compare whole numbers, fractions or decimals. You can also create your own activities, including ordering measurements with different units.

http://www.topmarks.co.uk/r.aspx?sid=2452

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/

Type in a length and a unit, and this website will convert your boring old unit to something much more interesting, eg 200 cm converts to 39 AA batteries end to end, or 10 five month old human fetuses end to end or even 1.4 standard railway gauges. Fun and educational. Three thumbs up!

http://www.sensibleunits.com/