Here's a list of the major features from the Kindle for Android website:
- Get the best reading experience available on your Android phone. No Kindle required
- Access your Kindle books even if you don't have your Kindle with you
- Automatically synchronize your last page read and annotations between devices with Whispersync
- Adjust the text size, add bookmarks, and view the annotations you created on your Kindle, computer, or other Kindle-compatible device
- Read in portrait or landscape mode
- Tap on either side of the screen or flick to turn pages
The Whispersync technology seems to be one of the most unique features of the Kindle app. It will synchronize where you last read on multiple kindle devices (iPhone, Android, Kindle, iPad). This a cool feature, that might help transition regular book readers into ebook readers.
You can find the Kindle application on the Android Market and the App Store for Apple Devices.