by Aldin Delić
Krita is a nice sketching and painting program. It is intended to allow users to create concept art, texture/matte painting, illustrations and comics. My favorite features are the perspective and vanishing point tools.
Check it out at:
Inkscape is an open source vector graphics editor similar to Adobe Illustrator. It has flexible drawing tools, broad file format compatibility, powerful text tool and bezier and spiro curves.