The way the relevant parts of sectioning commands work is exemplified
by the way the \chapter command uses the counter secnumdepth
(described in Appendix C of the LaTeX manual):
.aux file, which will appear in
the .toc;
secnumdepth counter is greater than or equal to
zero,
increase the counter for the chapter and write it out.
So a simple way to get headings of funny 'sections' such as prefaces in the table of contents is to use the counter:
\setcounter{secnumdepth}{-1}
\chapter{Preface}
Unfortunately, you have to set secnumdepth back to its usual
value (which is 2 in the standard styles) before you do any 'section'
which you want to be numbered.
Similar settings are made, automatically, in the LaTeX book class by
the \frontmatter and \backmatter commands.
The value of the counter tocdepth controls which headings
will be finally printed in the table of contents. This normally has
to be set in the preamble and is a constant for the document. The
package tocvsec2 package provides a convenient interface to
allow you to change the secnumdepth and/or the
tocdepth counter values at any point in the body of the
document; this provides convenient independent controls over the
sectional numbering and the table of contents.
The package abstract (see
one-column abstracts) includes an option
to add the abstract to the table of contents, while the
package tocbibind has options to include the table of
contents itself, the bibliography, index, etc., to
the table of contents.
The KOMA-Script classes have commands \addchap and
\addsec, which work like \chapter and \section but
aren't numbered. The memoir class incorporates the facilities
of all three of the abstract, tocbibind and
tocvsec2 packages.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=secnumdep