I linked this in my first post, but feared it wouldn't be noticed. There is a wonderful recent book by Philip Yancy on prayer, inspired by an article he wrote years earlier on "prayer/does God change?" Its a googlebook, most if it seems fully readable.
If you haven't read Yancy yet, check him out. He's one of the most graceful, broad, and intellectually vulnerable Christian writers I know, had the "emergent" spirit, I'd say years before any of us started talking about it! He recaptures so much of the richness of the Christian tradition and shares it so freely, you always feel he's completely honest and asking questions he himself has pondered for years. Many have hailed him as coming close to a next CS Lewis. :)
Reaching for the Invisible God, The Jesus I Never Knew and What's so Amazing About Grace are other classics. Soul Survivor is a personal testement to the authors and persons who have shaped his spiritual journey profoundly, from Henri Nouwen to Tolstoy/Dostoevsky.