If you're interested in merely adding ascii-art diagrams to your document, you can dump the ascii-art content in the verbatim environment:
\documentclass{minimal}
\begin{document}% Taken from http://ditaa.sourceforge.net/
\begin{verbatim}
+--------+ +-------+ +-------+
| | --+ ditaa +--> | |
| Text | +-------+ |diagram|
|Document| |!magic!| | |
| {d}| | | | |
+---+----+ +-------+ +-------+
: ^
| Lots of work |
+-------------------------+
\end{verbatim}
\end{document}
The verbatim environment typesets its contents as-is using the \ttfamily
font, keeping the alignment (whitespace).

If you're interested in a converted graphic/image (a ditaa
-processed version of your ascii-art), then importing a PNG (or JPG/BMP) from your ditaa outpout would be easiest. This, however, comes with a loss of quality in the output. If the EPS add-on is readily available, then using it to produce EPS images (or even converted to PDF) would achieve the highest quality. Here's a graphic from the website illustrating the difference in quality when using rasterized vs vector graphics:

Finally, TikZ/PGF
and PStricks
both provide a bounty of native drawing capabilities within (La)TeX. The TikZ/PGF
documentation is filled with examples, as is many of the package documentations associated with PStricks
. They each come with their own set of macros/commands that allow for drawing diagrams similar to those done by ditaa
.
The advantage of using native packages as opposed to some external application (like ditaa
) is that it provides the capability to alter an "image" within your (La)TeX code rather than using an external application as a stepping stone. Moreover, with (La)TeX being platform independent, such advantages of native programming add even more value.
\includegraphics
.