I've recently discovered this website and I've been using it to design my patchwork patterns for my Christmas projects.
I usually print off graph paper and colour it in
but this is a nice tidy way of doing and saving it online. You can work from a clear grid and do your own or download a pic.
It seems to be primarily for embroidery/cross stitch but can also be used for knitting and crochet. I pretend I'm doing cross stitch cos a square's a square.
Here.