You can get really creative by making them decorative items like wall hangings with poems written by you. Send them a bottle of wine or champagne with a small two liner poem engraved on the bottle. They will surely keep it forever. Similarly you can opt for personalized items like photo frames and photo albums with small stanzas written over them at different places. You can convert your small love poem into songs and sing it out to them. If you know to play any kind of musical instrument, it will only add to the magic.