The definition of \part and \part* in article.cls is:
\def\@part[#1]#2{% <------------------------------- \part[..]{...}
\ifnum \c@secnumdepth >\m@ne
\refstepcounter{part}%
\addcontentsline{toc}{part}{\thepart\hspace{1em}#1}%
\else
\addcontentsline{toc}{part}{#1}%
\fi
{\parindent \z@ \raggedright
\interlinepenalty \@M
\normalfont
\ifnum \c@secnumdepth >\m@ne
\Large\bfseries \partname\nobreakspace\thepart% Part font
\par\nobreak
\fi
\huge \bfseries #2% Title font
\markboth{}{}\par}%
\nobreak
\vskip 3ex
\@afterheading}
\def\@spart#1{% <------------------------------- \part*{...}
{\parindent \z@ \raggedright
\interlinepenalty \@M
\normalfont
\huge \bfseries #1\par}% Title font
\nobreak
\vskip 3ex
\@afterheading}
You can include these in your document and modify the "font" parts (highlighted above; "Part font" and "Title font") to your liking. There's also packages like titlesec and sectsty that can help. Using the latter, is as easy as
\usepackage{sectsty}% http://ctan.org/pkg/secsty
\partfont{\large\bfseries}
to change the "Part font" to \large\bfseries.
Expanding on the former (raw) LaTeX code, to change the font specifically for \part*, use something like
\def\@spart#1{% <------------------------------- \part*{...}
{\parindent \z@ \raggedright
\interlinepenalty \@M
\normalfont
\large \bfseries #1\par}% Title font
\nobreak
\vskip 3ex
\@afterheading}
where I've changed the \huge font size to \large, keeping it bold.
Remember to wrap the macro redefinition with a \makeatletter...\makeatother pair. See What do \makeatletter and \makeatother do?
LARGEinstead but spot on withsectstyapproach. Thank you. +1 – Tyler Rinker Nov 01 '12 at 00:58