We were having dinner with friends at a local restaurant when we mentioned to the server that it was Mary Ellen's birthday. At the end of the dinner the server brought a dessert that could be shared by all four of us. While we were enjoying the sweets another server came by with a Birthday Card. The card said simply, "thank you for sharing your birthday with us". The handwritten card was an unexpected hit and a physical reminder of the experience. Much more memorable than a group of servers singing Happy Birthday.
What are you doing to surprise your guests?