Ask HN: product roadmap drawing app?

My partners requested that I prepare and give them a product roadmap, with high level features described, time frames, etc. I'd like to be able to make this a little more detailed -- maybe diagramming out the existing relationships btwn the current database, show the request flow for a user, etc.

I've tried UML and Visio, and even Omnigraffle. None of those are quite what I want, which is more of a mix between omnigraffle, visio, and being able to show/reveal blocks of text.

What do you guys use for this? Is there a cool software package out there that makes this simple?