I've never made a sewing machine cover so I might not be the best person to respond to this but I'll give it a go. First off, if you google Oil Cloth, there is a ton of awesome sites with interesting and not so dated patterns on them. I only know this because I've been trying to come up with an interesting solution for my craft room floor so that I can spill paint and get messy without worrying. So far, making an oil cloth "rug" is at the top of my list.
As far as other durable fabrics, you could always try canvas maybe? Even decorate it yourself that way. But seriously, what do I know?
Good luck on your project!