Subtitle with the \maketitle page?

With the titling package one can define a \subtitle command as follows:

\documentclass[a4paper]{article}
\usepackage{titling}
\newcommand{\subtitle}[1]{%
  \posttitle{%
    \par\end{center}
    \begin{center}\large#1\end{center}
    \vskip0.5em}%
}

\begin{document}

\title{(Title)}
\subtitle{(Subtitle)}

\author{(Author)}

\maketitle

\end{document}

The trick is that titling redefines \maketitle so that it executes, among other things

<pretitle tokens> <title tokens> <posttitle tokens>

and what goes in <posttitle tokens> is set by

\posttitle{tokens}

The default, as made clear in the documentation, is

  \posttitle{\par\end{center}\vskip0.5em}

so what's needed is to insert something in between.

In the standard classes: no. In the KOMA-Script classes: yes.

\documentclass{scrartcl}

\begin{document}

\title{(Title)}
\subtitle{(Subtitle)}
\author{(Author)}

\maketitle

\end{document}