TeX can be used to generate publication-quality schematics. Here are some examples.
CircuiTikz is a set of LaTeX macros designed to make it easy to draw electrical networks in scientific publications. It provides a convenient syntax based on to-paths to place the various components.
Or generate them in PostScript in conjunction with TeX? I think these are similar enough to combine in one answer.
pst-circ is a PSTricks package to draw electric and electronic circuits. It can be used either with TeX or LaTeX.