Rest in Practice

It's a good solid book that goes over the different kinds of REST in order, and explains why it is that HATEOAS and MIME types are really the most extensible form of REST that you can use.

I would have appreciated more discussion of HATEOAS edge case such as batching and partial updates, and a more in-depth explanation of what a resource is and how to cut down on network round trips (this was a concern when writing an API that had to interact with a flash client, as starting a flash client and doing several HTTP round trips is not all that cheap). Still, for what it provides, it is far better than most of the other books out there, particularly the O'Reilly option.