Just an FYI, if you come up with a texture that isn't already tile-able seamlessly, it is very easy to touch up a graphic so it tiles without seams, folds, or borders. GIMP has a quick, easy "make tile-able" option that works on just about any graphic, even non-square ones.
If you don't know how to work GIMP, you can submit something anyways and someone else can alter it so it tiles/repeats better.