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.
But, at times, material things aren't always the perfect choice for the occasion. In the end, it is up to you to decide what kind of gifts you'd like to present to your husband, and basically, make his day. And remember, whatever gift you present to him should be something he doesn't already own and can utilize it on the day or in the future.