Perimeter
(outside)

Add the length of each side to get a rectangle's perimeter.

http://www.bgfl.org/bgfl/custom/resources_ftp/client_ftp/ks2/maths/perimeter_and_area/index.html

http://www.mathgoodies.com/lessons/vol1/perimeter.html

http://www.mathleague.com/help/geometry/area.htm#perimeter

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

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

http://www.math10.com/en/geometry/perimeter.html

http://www.shodor.org/interactivate1.0/activities/perimeter/index.html
Game
http://www.softschools.com/math/geometry/perimeter.jsp

http://www.mathplayground.com/area_perimeter.html