Shape Surveyor
This interactive site will give you some practice calculating perimeters. It is a bit elementary, but if you choose the "super brain" category, you can practice finding perimeters.
http://www.funbrain.com/poly/

Rectangles
This site can give you practice finding the perimeter of rectangles.
http://www.mathgoodies.com/lessons/vol1/area_rectangle.html

Polygons
This site can give you practice finding the perimeter of polygons.
http://www.mathgoodies.com/lessons/vol1/perimeter.html

Perimeter and Circumference
This site gives you some practice with some applied perimeter and circumference problems.
http://regentsprep.org/Regents/math/fperim/PracPer.htm