Here is the list of my favorite places to shop for diaper-making supplies.
http://www.sewzannes.com/ (great fabric, love the 80% cotton velour, 91% sherpa, PUL, Aplix)
http://www.diapercuts.com/ (great PUL, Aplix)
http://www.celticclothswholesale.com/ (great organic cotton fleece)
Joann's and Hancock storefronts (great faux minkee, fleece, microfleece, flannel, cotton print woven, etc.)