If you're looking for really challenging Calcudoku (also known as Kenken) puzzles, then look no further. From the reviews of volume I:
"I highly recommend this book for the avid solver." - JHackley. "These puzzles will keep you busy for hours. " - Rockman. "I have tried every difficult, advanced kenken and calcudoku book there is and this one is the most challenging." - Jorge Lobo.
This volume II has 121 new puzzles and many new puzzle variations (puzzles with exponentiation, without operators, extra large puzzles, etc.). It also features extended explanations of the variations on the standard puzzle, as well as step-by-step solving guides for two tricky sample puzzles.
The five largest puzzles are printed twice: once on a single page, and once on four separate pages so you can cut & glue to create a larger version.
You can submit your solution for each puzzle (except for the "warmup" puzzles) at calcudoku.org, and score 12 points for each correct solution!
Note that also in Volume II there are no solutions in the back (except for the example and "warmup" puzzles). If you do need a hint, the solution to a specific puzzle, or even all solutions, you can send me e-mail (address is in the book) and I'll send them as a PDF.