We are learning to use repeat patterns in our Integrated Design class. We are developing designs to use in our Screen Print, Knit and Weave classes (slightly different criteria for whichever is our focus). Today we were shown a free download program that produces repeat patterns. It wasn't designed for this purpose but gives endless play with the concept. It is called Escher Web Sketch and was developed for students studying chrystallography.
I have just downloaded it and quickly produced these patterns. I will have to have a better look at the program and see if I can come up with some pleasing designs.