C.J. Mahaney with some great thoughts here (and here) on modesty from his forthcoming book, Worldliness: Resisting the Seduction of a Fallen World (Crossway, Sept. 2008). Here's a couple memorable quotes:
There is “not a square inch” of our lives—including our closets—with which God is not concerned. Even more, he cares about the heart behind what you wear, about whether your wardrobe reveals the presence of worldliness or godliness.
Modesty is humility expressed in dress.