NPR
Non-photoreal rendering

*N*PR

Toon shading

Toon shading - howto

Pen-and-ink, drawing

Here is a paper that describes some of the techniques.

'Loose' style

Teddy..

Here is much, much more!

Stippling, hatching

This is Adrian Secord's paper on 'weighted Voronoi stippling'.

Tech. illustration

For a description of the Gooch shader, see p.87, from these SIGGRAPH course notes pages.

Stripes

Woodcut

Chalk

See Gershon Elber's papers, for more on this.

Cartoony

Oriental

Line and tone

Paint

Paint pipeline