often IT Admins who take care of networking and building infrastructure for Big companies require to draw maps on to explain how it will look when all hardware, severs etc will look when put together. Network Whiteboard is a free application which helps you design in such situations.
It creates a diagram which looks like a use case diagram except that you put across physical hardware in diagrammatic form. You can add your text and draw lines to explain it neatly. Download Network White @ Google Code