Aside from mathematics, chemistry seems to be the subject for which the most TeX packages have been created. Information on a few such packages have been linked below. There is also a system called ConTeXt, which is based on TeX, that includes a module specifically designed for the drawing of chemical structures and the typesetting of reactions called PPCHTeX. It is theoretically possible to have the same functionality with LaTeX by loading the
m-pictex and the
m-ch-en packages which are part of ConTeXt, but this is difficult to implement.
There does not seem to be many packages designed with the subject of biology in mind. Those which have been linked to below are related to genetics and graphically showing genealogical relations.
There is some overlap between the symbols and operators used in mathematics and physics, so many of macros in the
amsmath package will be of use in the context of physics as well. There are, however, a few specific packages related to physics, a few of which have been linked below.