I made this one last year-
There are so many ways to make rugs. Both of these are crocheted, but you can use the toothbrush technique if you want a more heavy duty rug.
You can braid t-yarn- http://sewliberated.typepad.com/sew_liberated/2011/01/the-rainbow-rug.html
Isn't this beautiful? It's from the above website.
(picture from Family Fun)
Or make a latch hook rug- http://familyfun.go.com/crafts/crafts-by-type/sewing-fabric-projects/no-sew-projects/hula-hoop-rug-995304/(photo from e-how)
One more thing, if you've gone through all of the dressers and closets in your house and people are starting to complain because they can't find a t shirt, thrift stores are a great source for more supplies. Our thrift store sells a whole bag of t shirts for $2!
I think the braided rug is next on the list. I love the colors that she used.