Title style is defined with beamercolor
and beamerfont
templates. Use them inside a beamercolorbox
with correct dimensions or just fix them before writing the title.
If you want also horizontally centre ordered or unordered lists, use varwidth
package.
Next is a modification of Christof's example. Adjust it to your stylish needs.
\documentclass{beamer}
\usetheme{Rochester}
\usecolortheme{beaver}
\setbeamercolor*{item}{fg=red!70!black!100!}
\useinnertheme{circles}
\usepackage{varwidth}
\newcommand{\mytitle}{
\begin{beamercolorbox}[ht=3ex,dp=1ex,center,wd=\framewidth]{frametitle}
\usebeamerfont{frametitle}\insertframetitle
\end{beamercolorbox}\begin{beamercolorbox}[ht=3ex,dp=1ex,center,wd=\framewidth]{framesubtitle}
\usebeamerfont{framesubtitle}\insertframesubtitle
\end{beamercolorbox}}
\begin{document}
\begin{frame}[plain]{Frametitle}{Framesubtitle}
\centering
\mytitle
\medskip
Some Text. Some Text. Some Text. Some Text. Some Text. Some Text.
\medskip
\begin{varwidth}{.5\linewidth}
\begin{itemize}
\item One Subject
\item Another Subject
\end{itemize}\end{varwidth}
\end{frame}
\end{document}

c
option to the frame environment:\begin{frame}[c] ... \end{frame}