Using the subfig package you can use tabulars to arrange the images:

\documentclass{article}
\usepackage{subfig}% http://ctan.org/pkg/subfig
\begin{document}
\begin{figure}[ht]
\begin{tabular}{c}
\subfloat[subfigure 1]{\rule{100pt}{50pt}} \\
\subfloat[subfigure 2]{\rule{100pt}{50pt}}
\end{tabular} \hfill
\begin{tabular}[m]{c}
\subfloat[subfigure 3]{\rule{100pt}{50pt}}
\end{tabular} \hfill
\begin{tabular}{c}
\subfloat[subfigure 4]{\rule{100pt}{50pt}} \\
\subfloat[subfigure 5]{\rule{100pt}{50pt}}
\end{tabular}
\caption{bla bla bla bla bla bla}
\end{figure}
\end{document}
Vertical alignment across the subfigures is obtained using the optional tabular parameter [m] for middle. Using \hfill as suggested will push the columns of subfigures to the outer edges of the text block. If you want these columns evenly spaces, use \null\hfill on the left of the first column and \hfill\null on the right of the last column. Alternatively, a fixed spacing using \hspace{<len>} is also possible, where <len> is any recognized TeX length.
tabular column specification necessarily adds a little horizontal space of \tabcolsep between columns. If you want this removed (for whatever reason), you can use a {@{}c@{}} column specification instead of {c}.