Although I've listened to "Getting Things Done" and "Ready for Anything" several times on tape, I still find the Covey books "Seven Habits" and "First Things First" to be the core of my life and time management philosophy. I find myself wishing that David Allen and Stephen Covey were working for the same company. I find Allen's "Ready for Anything" to be a great book of insights on how to better implement Covey's "First Things First." Many of Allen's insights are things that Covey himself is not that good at expressing, for example the Psychic RAM concept.
I have also learned a lot from Allen's book GTD. But where I part ways with Allen is in Chapter 9 when it comes time to make the decision on what to actually do at any moment. After 8 chapters of meticulous preparation in task organizing, I can't believe that Allen then just says "trust your heart" to make the decision. To me, this is exactly why I and others tend to manage time badly. I think that Covey's "perspective of the week" is where it's really at. If I were to just "trust my heart", I would spend all my time doing trivial things, and the truly important tasks would rarely get done.
The other book I've found helpful is Rita Emmett's "Procrastinator's Handbook."