For reasons "above my pay grade", we're developing an issue/project tracking system where I work (similar to Trac, FogBugz, etc). The managers want a useful tool to be able to track the overall health of the project (e.g. How much time left, how are we performing vs estimates) and one of the features that has been requested is some type of critical path support and visualization.

The logic explained to me is that they want to be sure that at least the most important pieces of the project are currently being worked on. The initial idea was that we would create task-based dependencies. My understanding of project management tells me that this kind of granular approach is unnecessary - having milestones with specific deadlines/dependencies is much more useful.

I would like to know what are the most useful techniques and "pretty pictures" you've seen/used for project development. Having objective data would be best, but somewhat subjective data is helpful too.