Amy Pederson P61315472-187x249
Missing Fabrics allows you to send in a piece of fabric for which you are searching.  The fabric is scanned and an "ad" for $1 is posted on the site.  The site claims a 70 % success rate.

Quiltshops.com is an internet group of independent quilt shops.  The search engine allows you to search 350,000 plus items at once for any item, with or without thumbnails.  It is particularly useful since it allows you to enter the fabric identification information from the side of the fabric for which you are searching.

The Fabric Depot is a large retail quilting store in Portland, Oregon which also has a very extensive on-line catalog.

Thousands of Bolts and Only One Nut offers fabrics at significantly discounted rates per yard.