For digital artists!
Halpful, handy, very cheap plugin for Photoshop-compatible editors - it's Engraver.

'Engraver - it is a plug-in module for the Adobe Photoshop and compatible editors.
This plug-in allows to stilyze any your photos or images as beautiful engraving pictures or pencil sketches. The Engraver allows cutting through images with thin lines that will form a geometric pattern. Using Engraver will let you represent your image as a colored or black-and-white stylized print.'