I have just purchased the airstechnologies professional package. It is absolutely brilliant, it takes you from ppl, cpl, irex and bgt. Basically they are lessons on Cd that are interactive, as you pass each section you muct get 100% to go to the next lesson.
I got it mainly for irex, it has improved my understanding out of sight. For an investment of about a thousand dollars it is worth it, this inetractive stuff is a lot better because you can retain a hell of a lot more information through speech, diagrams and text which is what this package is all about.
Good luck