InstantPhotoSketch is an easy-to-use tool for converting digital images (JPG, GIF, PNG, TIFF, BMP) into pencil sketches.
Trying this out can be as simple as opening your target file, and clicking "Create Sketch" (the green "Play" button in the centre of the toolbar). The program immediately transforms your image into a pencil sketch.
If you're not happy with the results then they can be tuned with the two sliders above the image. Reducing "black level" will produce lighter brush strokes, while adjusting "white level" appears to alter image brightness and contrast.
The Preview window updates in real time to show the effects of your fine-tuning. A Zoom tool allows you to focus on a particular detail, and once you're happy, the finished results may be saved as a JPG or PNG file.
InstantPhotoSketch is extremely basic, with only a single effect. This does work reasonably well, though, so if you're not happy with your current "sketch" effect (or you don't have one at all) then it's worth a try.