These are not paid advertisements, just the places I like to shop! :-)
Sewzanne's has a wonderful selection of knits, the site owners are the sweetest people and the shipping is lightening fast!
Super Buzzy has the best Japanese fabric selection in the US. Great prices and service!
Harts Fabric has a wonderful selection of domestic and imported fabrics and some great knits too. If you ever have the chance to get to Santa Cruz be sure to stop by in person. The store is beautiful and the staff is very helpful!
Etsy isn't just for handmade goods. It's a good place to find that rare, out of print fabric that is no longer available at retail stores.
More shops coming soon.