I needed some tiling patterns for a project I was working on. Having my priorities in order, I spent a night or so making a little program (read: Processing sketch) to help me draw such things. It's not super great for precision work, but it is super great at creating the world's tackiest patterns. Behold!
If you want to mess around with my code, go right ahead. (You'll need Processing to run this, though.) Scroll to zoom in and out, left click to draw, right click to fill, D to do a dithering fill. Up and Down brighten and darken, left and right select hue, and 1 and 2 affect saturation. (Yes, it's a pretty bad interface, but I didn't want to make a color picker.) B toggles the image borders, C toggles the little cursor dot, S saves the image, and N creates a new image. (All images have to be 64 by 64 pixels, but that's easily changeable in the source code.)
Happy tiling!