One of my very favorite Christian authors is Casandra Martin. She is the author of the Women Opening the Word bible study series. There are several studies in the series, each one inspiring, challenging you to become a better Christian. They truly make you take a deeper look at your faith and your walk with Christ and encourage you to become stronger and live purposefully. I recently finished up A Light in the Darkness. Although the focus of the study is on the prophets Elijah and Elisha, it encourages you to be a bright light in this dark world.
You can order the WOW bible studies from this website: 21st Century Christian, or if you're local, A&D Bookstore carries them.
"And do not be conformed to this world, but be transformed by the renewing of your mind, so that you may prove what the will of God is, that which is good and acceptable and perfect."
Romans 12:2 (NASB)