A friend of mine has the Kindle app on her IPuke. She doesn't own a Kindle and downloaded the app from the apple market. If my memory is serving me correctly, I think it was $4.99.
Amazon has announced that it will soon be porting it's popular Kindle App to the Android platform. The new Android book reader will also allow you to preview, and purchase books directly from Amazon’s Kindle bookstore all from the comfort of your Droid. While having the ability to run this app on an Android phone is nice, I think Amazon has another agenda and preparing for the release of many Android Tablets expected to launch later this year. Some of the features of the Kindle App will include: