In our uDig plug-ins for the Anaconda Workbench, we use Styled Layer Descriptors (SLD) for the map styles.
One of the features we are currently working on is the direction attributes for one-way streets. Of course you want to visualize them on the map, but SLD does not directly support arrow decorations for lines.
I asked for advice on the uDig mailing list and got the answer in no time. You can either use an arrow character from a suitable font in a Text Symbolizer, or a clever combination of Line Symbolizers with different styles of dashed lines to emulate arrows.
Using an SLD snippet from the Geoserver blog, I got the following result:
[Sorry, screenshot deleted to avoid potential licence issues.]