A favorite tradition at our house is one adopted from another family: a love-treasure hunt on Valentine's Day. I write a series of clues on heart shaped post-it notes leading to a small treasure & love note from me.
I write three or four clues for each person. Each clue is a simple rhyme, such as "Roses are red, violets are blue, look under a book for your next clue." When the kids couldn't read, I'd just draw a simple picture.
The treasure at the end of the hunt is a small organza bag with items like lip balm, chewing gum, legos, candy, action figure, tool, wind up toy, rubber stamp, or other such goodie. I make a Valentine/card to go with it!