I just took 3 references :

1) PMBOK guide - read it twice page to page .. Snce I had good exposure to CMMI implementation from scratch I could grasp everything quickly.

2) Rajesh Nair comprehensive notes - Its so nicely done, really very very helpful for another quick round of revision. Thanks to Rajesh for creating such a wonderful "all in one place" document. Its a concise PMBOK so to say !!