Amazon has built an iPod/iPhone optimized site for the hordes of people who have been buying ipod touches on their site.  It isn't overly functional but it works nicely.  The product scrolling is very cool as well.

You also have the ability to use the traditional browser experience to do your shopping inside the iPhone/iPod.

Amazon detects your browser type and adjusts the browser window accordingly.  They are also offering a generic mobile browser version of their site with considerably less functionality.

To get there, simply point your iPod/iPhone browser to http://www.amazon.com