Visit the Kentucky Educational Television Latin Distance Learning website! There you'll find Valentine's expressions in Latin, perfect for creating cards to share and exchange, as well as love myths from Greek, Roman and world mythology (most in English, but one in Latin, with vocabulary key and English translation), some Valentine's day trivia, links to some clip art, and a crossword puzzle! This is definitely a site that you must bookmark!
Also be sure to visit Rosa Latina, where Rose Williams has placed a collection of her holiday material. Here you'll find the Roman origins of Valentine's Day, a spring song of Love in Latin, as well as one of Catullus' famous poems.
Not Latin or Classics-related, but too cute are these do-it-yourself Heart-shaped Paper Clips! Get yourself a cheap multi-pack of colored clips at your favorite, local office supply store.