Are there good, reliable reference resources on the Internet?  Yes.  This list is by no means complete.  It is intended to give you a feel for what’s out there.
American Society for Indexing
http://www.asindexing.org/site/refbooks.shtml 
Council of Science Editors
http://www.councilscienceeditors.org/links.cfm
Fact Monster from Information Please
http://www.factmonster.com/science.html 
General Tables of Units of Measurement (NIST)
http://ts.nist.gov/WeightsAndMeasures/Publications/upload/h4402_appenc.pdf
How Many? A Dictionary of Units of Measurement
http://www.unc.edu/~rowlett/units/
HyperPhysics, HyperMath, HyperBiology
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
tcaep.co.uk  (constants […]

It seems that understanding and solving physics word problems is difficult for many students.  Here are some web pages that may prove useful.
Polya’s Recipe for Problem Solving
 Cooperative Group Problem Solving in Physics
A Logical Probelm Solving Strategy
Suggested reading:
Hewitt, Paul G. 2006 “Problems Without Numbers–at First”>  Science Teacher 73(5): 40-42.
Gaigher, E. 2007 “Exploring the Development of Conceptual […]