A romantic night out. A gift certificate for hotel and fancy dinner. Wrap it up in some other box to make it look like something else. Other people can go in on this gift if it's out of your price range.
A nice, hearfelt gift is a scrapbook or photo book chronicling the couples ten years together. If you don't have enough photos yourself, ask your friend's spouse to help you.
Tickets to a sporting event or a concert that the couple enjoys would be nice. Or if they drink, you could send a basket with wine, cheese, crackers, and dessert.
