the great decay

Aside from the Bible, John Piper's book 'don't waste your life' has had the most profound effect on me of anything i've ever read. Others come close, 'Desiring God', 'God is the Gospel', 'the shock of your life' and the 'mortification of sin' to name but a few, but this book gave the clearest and dearest glimpse of what Philippians 1:21 and Psalm 63:3 might actually mean.

desiringGod have just started to release DWYL vodcasts, (seriously, we've got to come up with a better name than that) you can see the latest one, as well as links to the others here.