Historical
The following website has interesting links on the history of thermodynamics and the development of steam power and how it transformed society and ushered the Industrial Revolution: http://www.history.rochester.edu/steam/
The Pneumatics of Hero.
The Galileo Project , here at Rice Univeristy, has interesting history information on Galileo, especially an account of a pump he invented for moving water with one horse. The page also mentions Galileo's conflict with Santorio Santorio over the invention of a prototype thermometer, a milestone in the history of thermodynamics.
Later, of course, steam power replaced horse power, as detailed in A History of the Growth of the Steam Engine by Robert H. Thurston.
The History of Hydraulics homepage at the University of Iowa has links to short write ups on Hero, Blaise Pascal, Bernoulli and Robert Fulton.
Reference
The National Institute of Standards and Technolgy website has a wealth of information, including definitions of SI units , a conversion program for energy equivalents and a searchable database of values of the physical constants.
Biological
Two great text-books are available online through PubMed Bookshelf : Molecular Biology of the Cell and Molecular Cell Biology
Mathematical
The Math Archives web site has numerous useful links to mine. A good review of math up through differential equations can be found at the Harvey Mudd College Mathematics Online Tutorial.
You can integrate any function at The Integrator
And of course, there is the
Matlab Support Site
Membrane
Biophysics