When it comes to online only shopping, obviously amazon.com is tops. I'm not sure other retailers understand how valuable the saved shopping cart (deferred ordering) and wishlists are for generating repeat business.
For a look at how a traditional catalog company turned their print catalog into a first-class online purchasing experience, check out mcmaster.com
. They have several physical warehouses, and in southern california, the delivery times are ridiculously short. It is worth placing an order just to experience the whole site design. If walmart, walgreens and whoever else knew what was up, they would be delivering online experiences at this level.