I'm not much of one for cards and flowers and that sort of thing. I also almost never give gifts. Every now and then the mood strikes me or I find a particularly appropriate thing for someone. It is a rare event, though.
With the help of Google, I found this web page: http://www.lonekeep.com/lki_home/Valentine.htm talking about the martyrdom of St. Valentine. It's pretty short, but the upshot is that, apparently, St. Valentine was beaten and beheaded for marrying young couples over the objections of Claudius II Gothicus, Emperor of Rome. The feast day of February 14 was made in honor of the martyr. (The date was probably influenced by various pagan celebrations happening around the same time. A practice common in the early Catholic church.)