Amazon have debateably one of the best iPhone optimised websites to date, and as of today, also have an iPhone and iPod touch application available. Along with all the usual features you"d expect from Amazon (purchasing goods, one-touch checkout, order checking), there is also something called "Amazon Remembers". Effectively, you can take a photograph of an item, send it to Amazon over the phones modem, or via wireless lan if you have an iPod touch device, and Amazon will try to identify a similar product for you to buy. They use a fold out chair as an example on their website, which you can find here.
(Seems to be available in the US only at the moment*)