My friend's husband took the shards of a decorative plate she had broken and had a piece made into a neclace. For her thiritieth birthday he sent some nice paper to all of her closest friends and family and asked them to create a page that captured something of their friendship with her. Then he had them bound into a book for her.
instead of buying her overpriced flowers, or the like, take her to a botanical garden. it's unexpected and original and won't cost more than 5 bucks. on a note, valentine's day is for suckers.
buy a couple of roses, and then tear off the petals and make a pathway with them to the bedroom. There....you wait with some cheap champagne. (perhaps in the bathroom)
Buy a nice vase, put twigs in it, and slip red, pink, and white hearts onto the twigs that say something special about her. It actually comes out quite nice with a little foilage added. Of course I think I ruined it by putting victoria secret panties around the base of the vase. But you gotta do what you gotta do.
