Cheryl Cage's Checklist for Success is awesome for every interview (especially for developing 'your stories' and avoiding common interview faux pas)
The old AIR Inc. book Questions, questions is good as well.
The best part of any interview prep service is the face-to-face or video evaluations. If you can get someone to video you answering questions it speaks volumes. You'll realize little ticks or quirks that you never knew you had. It also will tell you your strong points as well.