I just gave Imendio Planner a try. It's a simple (compared to MS Project) yet very useful project planning application. With Planner you can easily define ressources and tasks and compile them in a Gantt chart. The most important features are available such as four types of end-start conditions within the Gantt chart, assigning ressources to tasks, sub-tasks and more.

The tool has a nice simple GNOME GUI and seems to be a lot easier to use than MS Project. It lacks the (IMHO) important feature of displaying your use of ressources which is a pity. While it exports to HTML and prints nicely an option to export the Gantt chart to some graphics format might be helpful too.

Anyway I would use this in upcoming projects as its very simple to use, free, and fits into my usual development environment.