In the detective novels by Margery Allingham, her detective Mr Albert Campion has a sister called Valentine; however, since his real name is Rudolph, it's impossible to be sure that it's her actual name.
Valentine is the name of one of the central characters (played by Irene Jacob) in the film "Rouge" (1994) from Kieslowski's film cycle "Trois Couleurs." This may explain its sudden rise in popularity in France and Belgium in the last several years.