I tip my tri-cornered hat to Bill and Fr. Jim in pointing out that the pallium that Benedict XVI received during his inauguration is not of the type we are used to seeing, but is, in fact, closer to the form in use by popes during the first millennium, as Bill illustrates:
Pope Benedict XVI
Mosaic from Ravenna
Pope Innocent III
As Fr. Jim says,
The pallium is a very interesting vestment, tying the archbishops metropolitan throughout the world directly to the See of Peter and the person of the Pope.As you can see in the images, the original pallium is worn around the neck and drapes down the pope's left side. Compare that with the pallium worn by Pope John Paul II, which is smaller and drapes down the middle:
For more information about the pallium, check out the Catholic Encyclopedia (1917) article.