I second this. Very good tool for diagramming. All kinds of stencils / shapes / objects: Wireframes, UML, workflows, BPML,... Edit: And of course you can draw

I second this. Very good tool for diagramming. All kinds of stencils / shapes / objects: Wireframes, UML, workflows, BPML,... Edit: And of course you can draw free hand. It's vector based.