The first one is for the beginner. A great book for those who are just starting to learn SketchUp is SketchUp for Dummies. With about 250 pages to get introduced to all the basic SketchUp features and some more to start using some other intermediate procedures.
I think the "for Dummies" series can lack sometimes a bit of seriousness and the style of writing can be a bit confusing to get the information you want. But in this release they did a pretty good Job. The information is easy to follow, and the tutorials are good and you´ll learn some stuff that is not that easy to find on the online videos and tutorials. Yo can buy a hard copy in Amazon starting at $13.56 or a Kindle digital copy for only $9.99
The second one is a new release that looks like it might become a reference book for all SketchUp users. The Book is officially called "Google SketchUp and SketchUp Pro Bible", but my guess is that soon the SU community will know it as the SketchUp Bible. In this case you can for now only preorder a copy in Amazon for $26.39. Again, in this case I don't know if the book is good or not since it hasn't been released, it´s all from the guts in this case, but I am pretty good at guessing :P.
It comes with a CD with tutorials and reference files. I am planning to buy it soon, if you buy it before, please don´t hesitate to leave a comment about it. Thanks!