App: OmniGraffle for iPad
Developer: The Omni Group
OmniGraffle is an unusually expensive app, but it offers a spectacularly rich set of features. The app turns your iPad into a cocktail napkin, white board, or drafting table as you see fit. The toolset includes stencils and drag-and-drop convenience that makes it easy for busy network admins and architects to develop network diagrams on the go.