Why struggle with Visio or any other tool when yEd can do it all for you and takes no more than around five minutes to figure out?
Key features include:
- Import data for analysis from Excel spreadsheets or XML
- Create diagrams with ease using an intuitive user interface
- Auto-magically arrange your diagram elements
- Export your diagram to bitmap or vector graphics: PNG, JPG, SVG, PDF, SWF, ...
I've only used it for a brief while but the automatic layout wizard was enough to sell me on the product.
I strongly recommend it - try it out online here http://www.yworks.com/products/yed/demo/yed.jnlp or download it and try at home. Supports Windows, Unix/Linux, Mac OS.
Check out the promo video in 90 seconds here for a better advertisement than I can offer :)