For my IR, I'm using the Cessna Pilot Center version of the King course. They (John, Martha, and a few other corny people) are literally reading the textbook to me, and having to change my fonts every time I run the program and DVDs is driving me nuts. But in for a penny, in for a pound, and I'm not going to change this mid-stream, especially since this is the method used by my flight school. I do like the lab/flight system that they put together.
Because the knowledge is basic and minimal in this course, I'm supplementing this with the FAA Instrument Flying Handbook, and Rod Machado's new Instrument book, which is great, but probably twice the size if you took out the jokes. But, I like his style, and he makes complex concepts understandable.