While doing some research I was directed to the online bookstore Packt Publishing. Some other online book stores have a chapter listing, or a short excerpt. At Packt you seem to be able to download a sample chapter for every book you're interested in - at least all that I had a look at.
If you're a blogger you've also got the opportunity to review books. I've chosen one to review to see if it's worthwhile and let developers like you know if it's worth it. Stay tuned over the coming months, I hope to have it reviewed by the time the 2009 AUSOUG Conference series commences.
Online reference manuals are great, but sometimes you need more than a reference. I'm not a huge fan of books that regurgitate the documentation, but a best practices book or a guide to a new concept; case study or transformation process never goes astray.