In addition to most or all of the big-name brands, Marshall's Dry Goods sells a lot of the fabrics found at Walmart. Look in General Fabrics.
http://www.marshalldrygoods.com/store/
Crow's Nest Quilting specializes in Red Rooster but also carries some of the fabs found at Walmart, and some from P&B Textiles.
http://stores.ebay.com/CROWSNESTQUIL...Q_scZ1QQ_sopZ1
both sites have great prices and excellent service.