How can I add more than one logo to my beamer presentation?

Beamer provides \logo{} to set the logo(s). You could just add all three logos in there using three \includegraphics command (or PGF image commands). Where they are placed depends on your chosen scheme. If you want them a little larger on the title page you can insert the defined logo(s) manually \insertlogo e.g. inside a \scalebox.

The following code adds three scaled logos with one space as a separator into the right border. The default (blank) scheme puts them into the lower right corner.

\documentclass{beamer}

\author{Me}
\title{Presentation}
\logo{%
    \includegraphics[width=1cm,height=1cm,keepaspectratio]{logo1}~%
    \includegraphics[width=1cm,height=1cm,keepaspectratio]{logo2}~%
    \includegraphics[width=1cm,height=1cm,keepaspectratio]{logo3}%
}
\institute{Three Kings\\\scalebox{2}{\insertlogo}}
\begin{document}
\frame{\maketitle}
\frame{text}
\frame{}

\end{document}

you can have several logos on the page. The question is only where they should appear. Here an example for the second one in the sidebar.

\documentclass{beamer}
\usecolortheme{dove}
\useoutertheme{sidebar}
\pgfdeclareimage[height=2.25ex,width=2.5\baselineskip]{institut-logo}{zedat}
\pgfdeclareimage[height=1.3cm]{uni}{fu-berlin}
\logo{\pgfuseimage{uni}}
\setbeamertemplate{footline}{\raisebox{-2ex}{\pgfuseimage{institut-logo}}
  \usebeamerfont{date in head/foot}\insertshortdate{}\hfill
  \usebeamertemplate{navigation symbols}\hfill
  \insertframenumber{}/\inserttotalframenumber}
\setbeamertemplate{sidebar right}{}

\begin{document}
\begin{frame}{Das Logo}
\begin{block}{Ein Beispiel mit der Umgebung \texttt{block}}
Es ist offensichtlich, dass wir hier zwei Logos auf der Folie haben.
\end{block}
\end{frame}
\end{document}

from: http://tex.stackexchange.com/questions/18410/how-can-i-add-more-than-one-logo-to-my-beamer-presentation