Here's a great block idea and it's perfect for 5" and 10" squares.  Check it out!

This pinwheel block is so simple you'll wonder why you didn't think of it yourself.  Here's how it's made:

Make some half-square triangles.  Cut them in half vertically. Rotate one side 180 degrees and sew them together.  Trim to square, then sew four of them together!  How simple is that?

This is from a new book, Sew Simple Pinwheels by Karin Hellaby.  Karin has created four different techniques in one book and it's a bargain at $14.95.  She also shares several different setting and variations of the basic block. 

These books are on order and should be available within the next couple of weeks.  Try a few blocks and see what you think!