Many churches around the world will observe the Week of Prayer for Christian Unity January 18-25. The Week of Prayer, which as been held each year since 1908, is an opportunity for Christians to repeat the prayer of Jesus that "all may be one." This year's theme is "Open Our Ears and Loosen Our Tongues," from Mark 7:31-37.
A history of The Week of Prayer: http://www.ncccusa.org/news/070104wpcu.html
More info about this year: http://www.geii.org/