When I was trying to figure out what to do with our gapingly empty upstairs playroom, I hit on the idea of a giant round rug to counteract the rectangularity of the room.
Below: The green carpet is from Saxony Carpet in NY; they will cut rugs in any shape, round, oval, or even ovoid, if you give them a template. Approximately $2,500 for a 10-foot round carpet; go to Saxony Carpet.
Below: The spherical rug works just as well in an adult space. The stunningly chic Tribeca furniture company BDDW offers the Lawn Rug, a hand-knotted Tibetan wool carpet with alternating wool lines. Go to BDDW for information.
Below: The BDDW Tablecloth rug would be especially pretty in a lucky girl's room.
Below: Another round option from BBDW is the Wallpaper rug.
Below: Celeste Round Shag Rug from Crate and Barrel; 6 feet in diameter; $399.
Below: West Elm also carries a round wool flokati rug, starting at $299 for the 6-foot diameter rug.
Below: West Elm offers a round 8-foot-by-10-foot jute braided rug for $249.