I've always liked the disappearing four patch. Clean and simple, but so many possibilities. I like it more than the nine patch, personally. For an extra level of difficulty, if you're feeling brave, you could try doing the same technique with large half-square triangle blocks in a pinwheel shape. Sew the blocks together the same as you would the disappearing four patch, cut it the same, flip it the same, and stitch it back together. It makes a very intricate pattern with hardly any effort (besides the effort it takes to keep the pieces in the right place).