Some of the nicest I Spy quilts are the simple ones. A charm square quilt is made from many, many squares and no two squares are the same. Collecting the charms takes time and swapping with other quilters can speed the collection process.
One of the blogs I follow is Obsessively Stitching. I enjoy the quilts and other projects pictured, many of which are Quite Small. Her latest quilt shown above is a great I Spy. No sashing, no filler fabrics, just dozens and dozens of bright I Spy squares. This blogger runs charm square swaps for I Spy fabrics too, very handy if you want to increase your collection for your charm square quilt.