my all-time favorite on-line sites, in no particular order are:
stitch-n-frame.net She has a Thursday special each week and you can sign on for her reminder. Great prices, great service. I've shopped from Kay for years and years now.
hancocksofpaducah.com Ditto as above--been using them for years. They are more expensive now than before but have great sales and decent service.
equilter.com Though her prices are higher than most other sites, she has an absolutely unbelievable and extensive collection of fabrics with good service.