Saint Valentine's Day, popularly celebrated in the West on February 14th, was named after St. Valentine (or Valentinus, in Latin). This day, popular with romantic couples, is mired in mythology, and in fact, may not even be authentically named.
The Catholic Encyclopedia acknowledges that there were three martyrs named St. Valentine. Which one has been historically associated with February 14th is still in question and will probably never be resolved. One was a priest of Rome and another was a bishop in Italy. Both of these men were buried in Italy. A third St. Valentine was martyred in Africa; nothing else is known about him and extremely little is known of the other two.
But where history ends, legend begins. According to the legend of St. Valentine's day as recorded on the Norway Post's website
St. Valentine was thrown into prison and condemned to death in 270 AD because he would not deny his God. While he was in prison, he gave lessons to the jailer’s blind daughter, Julia, and taught her about God. One day while Valentine and Julia were praying together, a light appeared in the cell. “I can see, I can see!” Julia cried, while Valentine fell to his knees and thanked God. Before he was executed, Valentine wrote a letter to Julia declaring his love for her. On the day after his execution, 14 February, Julia planted an almond tree on Valentine’s grave.
Yesterday (Feb. 8, 2008) Norway issued a pair of St. Valentine's day stamps. The Norway-delivery stamp is shown in this entry. The European-delivery stamp, and ordering information, can be found here.