There is a great thread about this somewhere but here are a few suggestions. Each park has an "It's My Birthday" button - these are large (around 2 inches) buttons - not pins. You can go to guest services in each park and request one - they are FREE. The ones for MK and MGM I believe are the same. There is also one from Downtown Disney. We did this last May for my 40 something birthday. We received choice seating at Cinderella's Castle for lunch, a Magical Moments Certificate and a free desert, a free desert in Canada and a birthday card, a birthday card signed by Mickey and balloons's at our hotel, free desert at 'Ohana and probably some other things also. You also get ALOT of people wishing you Happy Birthday - both CM's and guests. I also had a name badge on so I received personalized birthday greetings. Make sure when you make your hotel reservations you mention the birthday, and also bring it up again when you check in. Also mention it when you make reservations for meals and also mention it again when you check in. Nothing is guaranteed but it is fun to do.
The other thing I did was to get a Passport from Epcot. When I had the CM's sign it from each country, they wrote Happy Birthday in their language. I used some of the stamps that came with the Passport but I also made sure to get a picture in each country of something specific from that country with either myself or my boyfriend in the picture, cut this down to size and put it in the Passport. This made a great small scrapbook.
Have a wonderful time.
Linda