Science:
Ice: http://www.cco.caltech.edu/~atomic/snowcrystals/ice/ice.htm
Water: http://www.lsbu.ac.uk/water
Engineering:
Hardware: http://www.mcmaster.com
General Information: http://www.efunda.com/home.cfm
Vacuum: http://www.lesker.com/
Mass Spectrometry: http://www.extrel.com
CAD/CAM: http://www.tecedu.com