My favorites:
Fat Quarter Shop
Missouri Star Quilt Company
Etsy- there is a seller called HunnieQuilt who has great prices and awesome service. I buy from her a lot. But there are other sellers there too, she's my favorite.
Shabby Fabrics- they also have nice tutorials on Youtube,
Green Fairy Quilts
I love to check out quilt shops when I'm out of town but don't buy much locally.