1 Corinthians 12 - The Miraculous Gifts of the Holy Spirit & Church Unity

In chapter twelve, Paul turns his attention to the miraculous gifts of the Holy Spirit. What does the Bible teach about the miraculous gifts, including gifts of healing, speaking in tongues, and the working of miracles? Are these spiritual gifts available today? Many Christians understand the miraculous gifts to have died within a generation of the Apostles. But is this what the Bible teaches?  

This passage also paints a beautiful picture of Christian unity within the body of Christ, a major theme in the book of 1 Corinthians. What can we learn from Paul about building a healthy, unified church?