In the latest Blender official version: 2.67, Freestyle NPR Rendering made it into Blender official builds (it was only available in test and experimental builds for a long time before). It works with Blender Internal Render and it allows us to create lines in the place of edges, contours, silouethes, etc.
This helps a lot creating 2D artistic renderings imitating drawings, cartoon effects, cell-shading... even create an image that looks like a blueprint from a 3D model. This last one is what we're gonna do in this tutorial :)
Original post at blendtuts: blendtuts.com/freestyle