Length (centimeters and millimeters), Mass (grams and kilograms), and Capacity (milliliters and liters)
http://www.teachingmeasures.co.uk/menu.html
Length in centimeters and inches
http://www.funbrain.com/measure/index.html
Centimeters, Inches, Ounces, Grams, Equivalent Units
http://www.gamequarium.com/measurement.html
Temperature in Celcius
http://www.bbc.co.uk/skillswise/numbers/measuring/temperature/quiz.shtml
Mass, Volume, Capacity, Length in Metric Units
http://www.bgfl.org/bgfl/custom/resources_ftp/client_ftp/ks2/maths/measures/index.htm
Metric Conversions
http://cemc2.math.uwaterloo.ca/mathfrog/english/kidz/metric4.shtml
Converting Units
http://www.mathcats.com/explore/convert.html
Measurement Quizzes
http://www.quiz-tree.com/Units_of_Measurement_main.html