I order from several different sites, but I like The Cotton Club best. If you're looking for Western themed fabric, try Stitchin Heaven, and if you like to buy fat quarters, go to Sweet Treats. They have individual fqs, but also sets of 8 fqs and lots of patterns for fq quilts. For Asian fabrics, I go to Sea Watch Fabrics and Shibori Dragon.
Also, I order from my local quilt shop online and then pick it up, so no shipping costs. This is great, because I can't get to them during the week, but know that on Saturday morning, I can walk in, pick up my order, and walk right back out.