Freestyle
Is a open source programmable stroke line (NPR) renderer that is being integrated into Blender 3d.
Made a complilation of my favorite line styled animation renders with SVN Blender2.50 Freestyle renderer build.
Most of these shots are done with Orthographic camera on to get a more flatten 2d effect.
Freestyle site
freestyle.sourceforge.net/
Blender integration blog
freestyleintegration.wordpress.com/