I broke down and splurged on a spiffy plug-in for Photoshop, called Symmetry Shop from Artlandia. They also have one for Illustrator called Symmetry Works. It cost me more than a few pennies but man is it fun! You can play with images and arrange all sorts of cool patterns with it. I just replaced my blog background with the first one I generated (if you see the old red one, hit refresh until it changes). I'll probably pop out a bunch more as I play around and try to get the hang of how to use it. And maybe a new banner while I'm at it... the current one has been up there a long time!
ps - hmmmm... this would be helpful if someone were, say... designing a line of fabric or some such silly thing. ;o)