If you know the couple and their taste well, something to add to their new home (still new for the first year) together such as art.
Also, many couples either because they are young and cash-strapped or because they lead really full lives might not have as much opportunity to do one-on-one outings as they would like. So tickets to some event they would both enjoy, a sporting event, music, a play, a gift certificate to an excellent restaurant would probably be very well received.
Another take on celebrating their romance would be a picnic kit with dishes that you could then add a bottle of wine and some delicacies to—to prompt their first use of it. These are available in all price ranges and types. Plus, they have the added advantage of being “green” in that they save the user from having to use disposable plates, cutlery, cups, etc.