A letter telling your parents of all the things you are grateful for. Make breakfast for them, or in the evening, cook a nice meal and set up a table outside with candles. Get them two movie tickets or tickets to a concert or play that they would like to watch.
You wouldn't forget the day you were getting married, so make it a point to celebrate the anniversary of that very special event each year. How you celebrate the anniversary depends on many factors. Can you find a babysitter? Can you book that favourite restaurant? If it's a surprise, will it be a welcome one?