It's excellent to see an array of Java programming books now available on the Kindle. Various of these books, which you may not have considered buying due to their cost, are available at a sometimes significantly reduced price on the Kindle.
Of notable interest to Javamex readers will be Brian Goetz's venerable Java Concurrency in Practice, which is really something of a bible for information on the Java Memory Model and the Java 5 concurrency library. As I say in the review, I can pretty much guarantee that if you're writing concurrent code (as many of us either are or will soon have to, not just on the server, but increasingly client-side), then Java Concurrency in Practice will allow you to fix various bugs in your code that you were possibly unaware of (it certainly fixed some in mine!), as well as help you make decisions about how to architecture your program around the Java 5 concurrency utilities.
For a more light-hearted read, but still an extremely enlightening one, Java Puzzlers remains excellent as ever. Josh Bloch's Effective Java got a whole new lease of life when its second edition was published, and its addition to the Kindle repertoire is most welcome.
Also worthy of note are the Core Java books. These, and in particular the second volume of Advanced Features, is not the most succinct of works, but covers various Java topics that you don't readily see explained in detail in other books.