People keep asking me about when we will publish the "definitive guide" book for symfony 1.4. We already have quite an extension documentation on symfony, but the definitive guide has a different way to teach you symfony that is best suited for some people. So, in the last few months, I have updated it to match the current version of symfony.
This new book includes a few things that some of the others don't like some time spent describing the philosophy of the framework and chapters for each feature of the framework (so that finding the documentation you're looking for is easier). You can get the book in print from Amazon or you can read it online for free.