PlaidMaker, an online tool that lets you design your own tartan. Pixels mimic threads, and you can create subtle patterns at a tiny scale, or bold prints in wild colors. Start from scratch or check out the gallery of user-generated plaids and modify any you like. Then download a .png file that will tile seamlessly. Use it for website backgrounds or wallpapers. Or, once you've got it tiled across a screen, you could take a screenshot and use it for your Facebook cover image.