As engineering is often all about knowing where to find  the reference or the formula, here are some excellent sites:

http://www.engineersedge.com/

http://www.modernplastics.com/default.htm

http://www.mfgquote.com/

http://www.rotomolding.org/

http://amsd-www.larc.nasa.gov/meweb/design.html

http://www.precisecast.com/