Suppose that the editor of your favourite journal has specified that section headings must be centred, in small capitals, and subsection headings ragged right in italic, but that you don't want to get involved in the sort of programming described in section 2.2 of The LaTeX Companion (see TeX-related books; the programming itself is discussed elsewhere in this FAQ). The following hack will probably satisfy your editor. Define yourself new commands
\newcommand{\ssection}[1]{%
\section[#1]{\centering\sc #1}}
\newcommand{\ssubsection}[1]{%
\subsection[#1]{\raggedright\it #1}}
and then use \ssection and \ssubsection in place of
\section and \subsection. This isn't perfect: section numbers
remain in bold, and starred forms need a separate redefinition.
The package sectsty provides an easy-to-use set of tools to do this job, while the package titlesec has a structured approach based on redefinition of the sectioning and chapter commands themselves. Titlesec's approach allows it to offer far more radical adjustment: its options provide (in effect) a toolbox for designing your own sectioning commands' output.
The fncychap package provides a nice collection of customised chapter heading designs. The anonchap package provides a simple means of typesetting chapter headings "like section headings" (i.e., without the "Chapter" part of the heading); the tocbibind package provides the same commands, in pursuit of another end. Unfortunately, fncychap is not attuned to the existence of front- and backmatter in book class documents.
The memoir class includes facilities that match
sectsty and titlesec, as well as a bundle of
chapter heading styles (including an anonchap-equivalent).
The KOMA-script classes also have sets of tools that provide
equivalent functionality, notably formatting specifications \partformat,
\chapterformat, \sectionformat, ..., as well as several
useful overall formatting specifications defined in class options.
Finally, the indefatigable Vincent Zoonekynd supplies examples of how to program alternative chapter heading styles and section heading styles. The web pages are not useful to users unless they are willing to do their own LaTeX programming.
The documentation of fncychap is distributed as a separate PostScript file.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=secthead