Fun Intro to Metric Measurement: http://www.mathsisfun.com/measure/metric-system-introduction.html
PBS Kids - Variety of Measurement Games (includes estimation on some!): http://pbskids.org/games/measurement/
Study Jam - Learn about measurement, sing karaoke, and practice/quiz yourself: http://studyjams.scholastic.com/studyjams/jams/math/index.htm
Funbrain Measuring game: http://www.funbrain.com/measure/
Comprehensive Explanation of Measurements, conversions, etc.: http://www.factmonster.com/ipka/A0876863.html
Temperature Units Comparison Chart (Fahrenheit, Celsius, Kelvin): http://ww2010.atmos.uiuc.edu/(Gh)/guides/maps/ctof.rxml
Online Length Unit Conversion: http://www.unit-conversion.info/length.html
Online Density Unit Conversion: http://www.unit-conversion.info/density.html
Online Volume Unit Converter: http://www.engineeringtoolbox.com/volume-units-converter-d_1034.html#.UpExX_mkr0d
About Heat and Temperature and how they're measured: http://coolcosmos.ipac.caltech.edu/cosmic_classroom/light_lessons/thermal/
2/19: Study stack: Metric words to know: http://www.studystack.com/flashcard-1329323
Triple beam balance practice/tutorial http://www.wisc-online.com/Objects/ViewObject.aspx?ID=GCH202
Spring scale lab: http://phet.colorado.edu/sims/mass-spring-lab/mass-spring-lab_en.html