Thankfully, due to the way I work and the 'clients' I work for I have few requirements to diagramme the applications I work on. However, there is the odd occassion where I need to create documentation for less (or traditionally) technically-minded people.
This usually results in me pulling out OmniGraffle or Visio and fighting with GUI-based design tools for presentation that really just represents fairly simple relationships, but I think I've found an answer.
yUML is a UML digramming tool that uses a simple, text-base DSL to describe your diagrammes, rather than fighting with mice and grids to get everything to fit together nicely.
For example, the below diagramme is generated with this very simple code:
If you want a simple, command line script to generate these images, check out the yUML Me Gem (although you will have to install Gemcutter first).
yUML can also make class and activity diagrammes, so check it out today.