Diagrams; either you love them or hate them. For those who have been around long enough to become Visio experts, you might actually appreciate that you can get the same kind of output from an entirely free tool, Diagram.ly. With numerous features and an easy web-based interface, here is another tool to your work anywhere, with any computer quiver!
No need to sign up and no fees make this a really great tool! Head on over an take a look, I'm sure you'll feel the same way I do!