Patternify is a simple pattern generator. built to save the pain of launching Photoshop just to export a 2px by 2px stripe pattern. Not only can you build your pattern online, but with the base64 code, you don't even need an image file anymore: just include the code in your CSS and you're ready to go!
Draw your pattern on the grid. You can use the cursors to limit the drawing surface and control the tiling. Once you're done, just download the PNG (make sure to rename it and add the ".png" extension at the end) or copy the code to your CSS. And you can also get a unique URL to share with other pattern aficionados.