Pack a picnic and go to the park. Act a bit like kids again, and swing on the swings, feed the birds any leftover sandwich crusts.
( okay, you have to pay for the food, but you need to eat anyway?)
Go for a long walk at sunset - make sure you hold hands
Recreate High School prom night in your own home...get all dressed up, put on some slow music and waltz the evening away - sort of sappy, but sweet
Make your wife breakfast in bed...make enough for you both and have a lazy morning in bed.
Check out your local community center or library for a fun, free classs or activity that you might both enjoy - new, common interests are good.