John Paul the Great. According to tradition, there are only two Roman Catholic popes who have been accorded the title "The Great." John Paul the Second (or Ioannes Paulus PP. II) should be known as John Paul the Great.

Now he belongs to the ages...

Update:

Father Richard John Neuhaus makes the case here.

Also, Cardinal Angelo Sodano, in the Requiem Mass for Karol Wojtyla, refers to him as "the Great."