Here are 7 free patterns that are some of the better looking I've seen. I like the one from Spool because my machine is married to it's extension table so I just need a mini-cover (you know, short like a mini-skirt) that fits the part above the table.
http://www.favecrafts.com/Home-Decor...achine-Covers# There are lots of other free patterns if you don't like these.