Windows only: Freeware application FotoSketcher takes your photos and turns them into pencil drawings, oil paintings or sketches—with impressive results for very little effort.
Using the application is easy enough—just launch it and drag a picture onto the interface, or open a new image from the File -> Open menu. Once you've pulled up the image, use the Edit -> Drawing parameters menu item to choose the filter you'd like to use, tweak the filter settings, and click the Draw it button to render the final drawing.
Readers will note that you can do the same thing from your fully licensed, totally legal copy of Photoshop, but for people without hundreds of dollars to spend, FotoSketcher produces some impressive results, easily, and for free. FotoSketcher is a free download for Windows only.