365 reasons why I love you jar. Both have their own jar and write once a day one thing they love about the other. On their anniversary/birthday/valentine's day/christmas/whatever the occasion, open the jar and read what the other person wrote
Great New Year's idea: Start the year with an empty jar and fill it with notes about good things that happen. Then, on New Years Eve, empty it and see what awesome stuff happened that year. Good way to keep things in perspective.