Links

Videos

Metric and Standard Measurement Systems  (time: 5:05)
http://www.youtube.com/watch?v=DQPQ_q59xyw

Metric Conversions (time: 4:08)
http://www.youtube.com/watch?v=XS-8FCqYo5M

History

This is one of the best all around sites that I have found. It is titled "The MacTutor History of Mathematics Archive."
http://www-history.mcs.st-and.ac.uk/~history/

This is an award-winning site that links to all sorts of mathematics information.
http://archives.math.utk.edu/

These sites are dictionaries of units of measurement.
This site has many nice links to other sites.
http://www.unc.edu/~rowlett/units/index.html

Reference Topics

"Go Metric," a site by the U.S. Metric Association; there is a lot at this site:
http://lamar.colostate.edu/~hillger

Temperature is discussed at this site:
http://www.allmeasures.com/temperature.html

Unit conversions:
http://www.m-w.com/mw/table/metricsy.htm

The following two sites are dictionaries of units of measurement:
This site has many nice links to other sites.
http://www.unc.edu/~rowlett/units/index.html