The Gleim book only tells you the answers to the questions.
You won't really learn anything from it and you need a good grounding on the subjects as the Instrument Ground portion of the PTS with the DPE/Examiner is quite indepth and can last a good couple of hours.
Hence why I said:
To actually learn the material, I suggest the King Schools computer based instrument course. It might be cheesy but you'll learn a lot, and you'll learn what you really want to know for real instrument flying, not just answers for an exam.
The Sporty's and Jepp stuff is good, but I also found it a little dry. Just my 2 pence