St. Valentine's Day remains the most popularly celebrated saint's feast day, even though his day has been formally stricken from the Church's calendar. Nothing is really known about the historical Valentine - there were actually two of them, which have pretty much been conflated. Both were (supposedly) tortured and killed by Roman Emperors. But no one really has any idea.
Above, you can see his skull (maybe).
He can be invoked against plague, epilepsy and fainting.
Now, go out and buy those cheap, marked-up, long stem roses!
(photo via Mymuk's flickr stream)