There are some great spectrum, or rainbow, quilts on the various web sites (like Flickr and Pinterest). Their simplicity (but in no way simplistic) really appeals to me.
I participated in an online spectrum charm swap and have put the 5" square together in half square triangles and tried to arrange them in order form darkest to lightest. Sometimes it worked out. I had quite a few left over (like I received way more orange than any other color) so I think I am going to make a few pillows to go with this quilt.
I was assigned yellow/green as my color and sent in a half yard of each color cut into 5" squares. I got a package back with one from everyone else who participated. Such a great trade I think.
I am participating in an eye spy swap too. This time I sent in a yard cut into charms. We had to put a picture of our fabric on the swap flickr site so we could make sure there weren't any duplicates.
Have you participated in any on line swaps?