Perhaps the simplest single block design is the basic repeated square. Here's an example in a batik quilt that I completed last year:
I made this quilt for "Quilts for Japan," a volunteer project based in Alberta that launched a drive to send quilts to the victims of the terrible earthquake and tsunami that took place in March. As someone who works with and admires Japanese textiles so immensely, I felt a special responsibility to contribute. I hope the quilt made someone's life just a little bit easier, even if only for a moment.