I think the L (left), R (right), and X (cross-hatch) patterns are the only ones, besides solid ones (using colors, or shades of gray).
One other possibility - if you have various pattern samples in an image file,
you could use that image as the fill pattern (assuming it's a 2d bar chart,
not a 3d one ... and maybe a few more limitations & gotchas).
The pattern statement would be something like the following (the color only comes into play, if the image file can't be found)...
pattern1 color=blue v=s image='random_pattern.gif' imagestyle=tile;