I use yEd for nicely organized diagrams (state diagrams, data flow, process models), Dia for information-rich structured diagrams (UML or network schemas), grap

I use yEd for nicely organized diagrams (state diagrams, data flow, process models), Dia for information-rich structured diagrams (UML or network schemas), graphwiz for autogenerated diagrams and Inkscape to make final touches to any of those.