Aside, take a look at tools like PlantUML as a way to create your diagrams. It's higher-level than, say, rolling everything with Graphviz, while easier to share and edit than a bunch of PowerPoint/Visio/etc. files.
The great thing about generated-diagrams is that you can easily store and version the original text representation along with the code it describes or applies to.
Mostly these were white boarded, but essentially I/we would draw a collaboration diagram (although I could have sworn these used to be called something else). They showed what data was needed to make certain decisions (eg, a conditional drop down that is populated based on another piece of data, or complex validation steps) and where to get data that already existed.
Yeah it looks like the activity diagram was substantially altered in UML 2.0. What we called an activity diagram then looks more like a collaboration diagram now.
