The Mitered Square Rug from Interweave! The free pattern is a lot of fun and a fair amount of work as well.
The picture on the top is the one my mom made, and it is posing on a tabletop so it can seen easier. Don't be frightened of the spine, she's a physical therapist.
The lower one is the one I made with different colors. Neither one of us used the colors in the pattern, though they are lovely too. We knitters are limited to the choices available, no?
If you adore weaving in thousands of loose ends, give it a go. We're almost at the end of cotton knitting season, people. Fall is right around the corner.