I bought this book when it was first released - very useful for two reasons: it describes different algorithms and their runtime for many common tasks, and, it is very short and is set up for quick browsing for what you need. Very good of the authors and publisher to release the PDF.
I especially liked chapters 1-3 which are very good introduction to MapReduce, those chapters focus on non-text processing related aspects of MapReduce. Also it is very short, and free.
