I left a little piece of my heart in so many of the places I visited and I've loved so many of the people I met in those places. These I Left My Heart In... cards from Paper Pastries are perfect for keeping in touch with long-distance friends made on world travels. Although it's not travel related, I especially love their I Left My Heart in the Library card.
Another great product from Paper Pastries on Double Takes blog: Home State Pride Return Address Stamps
(images vis Paper Pastries)