If you're looking for something a little different for a background in Adobe Illustrator, try holding down the Tilde (~) key while dragging out a shape using one of Illustrator's shape drawing tools such as line, circle, square, etc. Holding the Tilde key forces Illustrator to repeat the shapes in rapid fashion as you drag your mouse around the artboard.

For fun, I set all the shapes to the same color, then went back and randomly chose a few dozen shapes and made them a different color, then set all shapes to Multiply in the Transparency panel. Try it and you may find yourself busy for an hour or so.
Thanks to BittBox for the tip.








If you place a PSD file with a transparent background into Adobe InDesign and export it as a high-res PDF, you may notice that the edges of your placed image look horrible. There's usually a black & white halo around the edges of the transparent PSD (see the image above for example). You won't see them on a placed TIF file, and they generally don't print anyway, but they're annoying nonetheless.
