I just bought a "Raggy Rails" kit at a local LQS. Flannel front and back and something called "onsberg" for the center. Onsberg is a larger weave cotton that frays wonderfully but, is very light. I love how the quilt turned out. Only difference is you cut the onsberg the same size as the rest of the blocks so that it is included in the seam.
I have also done rag quilts with no batting and liked it also. Guess it depends on how heavy you want the quilt to be. I've also used fleece instead of batting and that worked very well. Very soft and cuddly. :)