My two favorites are equilter.com and zandsfabrics.com. Equilter has just about everything! (well in cotton prints anyway). I like zand s becasue they have cheap prices. I haven't had any problems with either company. Both have great customer service.
I buy 99% of my fabric online. It is more expensive, no denying that, but the quality is usually 200% better than anything I've ever picked up at Walmart. ZandSfabrics.com who sponsors craftster usually has really good prices. *and no, i'm not affilitated with them, but I do shop there*