EDITED so that this approach supports hyperlinking of subfigures.
Just replace the \rules with \includegraphics and put in your own captions. The gap between subfigure and subcaption can be changed with an optional argument (e.g., [5pt]) to \stackunder in the definitions of \capfiga, b, and c.
\documentclass{article}
\usepackage{hyperref}
\usepackage{stackengine}
\usepackage{subcaption}
\begin{document}
\begin{figure}
\centering
\def\figa{\rule{1in}{1.1in}}
\def\figb{\rule{2in}{3.4in}}
\def\figc{\rule{1in}{0.9in}}
\def\capa{subfig a caption}
\def\capb{subfig b caption}
\def\capc{subfig c caption which may be longer}
\savestack{\capfiga}{\subcaptionbox{\capa\label{fg:a}}{\figa}}
\savestack{\capfigb}{\subcaptionbox{\capb\label{fg:b}}{\figb}}
\savestack{\capfigc}{\subcaptionbox{\capc\label{fg:c}}{\figc}}
\def\hgap{3ex}
\stackon%
[\heightof{\figb}-\heightof{\figc}-\heightof{\capfiga}-\depthof{\capfiga}]%
{\capfigc}{\capfiga}\hspace{\hgap}\capfigb%
\caption{This is my figure\label{fg:}}
\end{figure}
\clearpage
In figure \ref{fg:}, \ref{fg:a}, \ref{fg:b} and \ref{fg:c}...
\end{document}

subfigurepackage I recommend switching tocaptionandsubcaption. I am looking for an example, where i used this and will post it in a bit. – Martin - マーチン Jul 18 '13 at 11:16