Shopping stores were dictating terms before a bunch of guys decided to start a marketplace that could increase the purchasing power of the customer manifold by launching a portal named e-bay. Not that there was a dearth of marketplace, they were in plenty and everybody had focused on either B2B or B2C but e-bay realized the true potential of having a C2C marketplace (with specific focus on how to sell second hand stuff with their selling tips) and end users embraced this concept with open arms.
Each of Amazon, Citibank, Sears, Overstock have epitomized online selling and are continuously transforming themselves to meet the end customer needs.
While amazon claims that they are the biggest seller on the earth and there logo signifies they can sell anything from "a" to "z" with an arrow going from a to z and living up to the expectations of being the No. 1 book sellers the latest to come from their stable is a "Kindle: Amazon's New Wireless Reading Device" which is a Revolutionary electronic-paper display provides a sharp, high-resolution screen that looks and reads like real paper.
Overstock on the other hand with its over sized "O" to signify that they have all thats in this sphere which is directed towards the shape of the earth and, now are close to the real world when they advertise on the net that "Carlos Boozer " who would be playing for US in the Olympics '08 is sponsored by them.
Sears typically plays with the human mind of buying products only when they see a discount available on it through any form. Hence they have promotions of Sales and Coupons on their website and its affiliates. So if we look at it the typical advertising angle of "Aware-Interest-Trial-Adoption" Sears focusses directly on Adoption as they know that giving discount coupons would immediately take an user to the last hurdle of purchase if they are really interested in buying a product.
There's never a famine of examples and if you pick up any of the Marketing books you might see all these compani"e"s listed in them, but the point that I am trying to drive here is that how these companies are continuously enhancing themselves to live upto the expectations that have been set on them by the users and how competition is making them evolve continuously.