AMZ Tracker is the only keyword rank tracker for Amazon in existence today. It allows you to quickly track hundreds of keyword rankings inside of the Amazon search engine. This allows you to keep track of what is ranking well, and what can use improvement. Works for Amazon as well as the Kindle Store, and it supports a variety of different countries.
AMZ Tracker also has a unique Amazon keyword generation tool integrated that will allow you to discover untapped keywords ripe for targeting on Amazon.com.
Come check us out, we have a free account for everyone.
Update* We have now released a new free Amazon product research tool called Unicorn Smasher. If you're looking for new products to sell on Amazon, we promise you'll love it :)