There are not many traditional quilt blocks whose name begins with X. perhaps one or two. In my research I went to a favorite website of mine, the Quilter's Cache, run by Marcia Hohn. She has a wealth of traditional and original quilt patterns there, all with accurate templates and well written instructions.
I respect her copyright, and so I am posting here links to her web pages, and not the images of the quilt blocks themselves.
X and Square
X's and O's
X - squared
And there are many more! I will be back to this site for Z.