Fabric sources?

I love the idea of sewing sweatpants that would actually fit my lanky girls for fall. I'd love to get some tips on where to find good quality cotton sweatshirt fleece, especially with cute prints like the stars and the floral design. Last fall I bought some (inexpensive) fleece from "that huge online store" and am pretty disappointed in its quality. Some cute fleece that has a soft feel on both sides and resists pilling would be great! What are your favorite sources (USA) for good quality knits?