Clark Aviation Consulting.
Without their help, my first "dream shot" interview ran off the rails and I didn't get the gig.
With their help, I am 2 for 2. :-)
Also when I did my last prep in March 2013, she said her clients had all been hired for the year...30 in a row so far at that time:
Airline Pilot Interview Preparation
I've read "Checklist for Success" and honestly wasn't that impressed.
After a prep course, I practice by sitting in front of a mirror in an empty room and blasting myself with the common interview questions at random to see how I answer them. Usually what I want to say and what I actually say are two different things, so practice practice!