Dickerson, Gray, and Haight:  an excellent general chemistry text,
included in the huge "Caltech Authors" archive
http://authors.library.caltech.edu/25050/

Digital Fish Library -- anatomical Magnetic Resonance Imaging at UCSD
http://www.digitalfishlibrary.org/

NIST physical reference data
http://www.nist.gov/pml/data/index.cfm

"Computational Knowledge Engine"
http://www.wolframalpha.com/

Water structure and science
http://www.lsbu.ac.uk/water/index2.html