There are so many, and I've tried numerous ones! I found many of them thru Quiltshops.com
http://www.quiltshops.com/
My favorites include:
Over the Rainbow
Desperate Quilters
Quilt Fabric Closeouts
Thousands of Bolts
Fabric Shack
River City Quilts
Hidden Country Quilts
Stitch-n-Frame
Whittle's Fabrics