Here is a link to an Advent Devotional Book that you can download for free from Desiring God.

The back cover of the book reads:

Advent is for adoring Jesus

It is a season of preparation for that special day when we mark
Immanuel’s arrival — the coming of our eternal God in frail,
human flesh.

This is the greatest wonder of history’s many wonders, something
too stupendous to celebrate just on one day. Advent is a
way of lengthening the joy of Christmas.

These 25 brief devotional readings from John Piper begin on
December 1 and carry us to Christmas Day. Our prayer is that
God would use these readings to deepen and sweeten your adoration
of Jesus this December and keep him as the center and
greatest treasure of your Christmas season. The candles and
candies have their place, but we want to make sure that in all
the Christmas rush and hubbub we adore Jesus above all.

http://www.desiringgod.org/blog/posts/good-news-of-great-joy-daily-readings-for-advent