During Networking subject, I search for network routing diagram and accidentally find online diagram editor – Gliffy. In this site are many powerful tools to create good locking and even complicated diagram for Web site/Software design, Venn diagrams, Org Charts, Network diagrams even home floor plan or business planing and more.
Basically its most popular browser-based applications, stuffed lightweight and low learning user interface. Gliffy easy to use, because its simple drag-and-drop interface, very similar like desktop software. There are a lots of information, for beginners and advanced users. Also huge library of standard icons.