Here are some sites I know of. I have just bought fabric from Maloufs fabrics and they were reasonable and fast!
www.maloufsfabrics.com
www.seawatchfabrics.com
www.burkholders.com
www.fabricshack.com
We need to have a comprehensive list for everyone. I have found other sites when searching for a specific fabric.
Hopefully I have spelled all these right
Lynda