Browsing Kindle books using Amazon's mobile site is so much more usable than on their main site.

Here's a screenshot using the iPod Touch:

It's clutter-free, yet still contains the info you need. You can buy books directly and send them to that same device.

The recently released Cloud Reader App does have a better integrated store, but for the time being that only seems enabled for US users. In the meantime, as a UK customer, mobile browsing provides the best Kindle experience.