From your post, I wasn't sure if you were looking for some extravagant event, or a nice way to celebrate, so I'll tell you the latter:
I turned 50 at Disney and the way we celebrated was by going to the 50's PrimeTime, because (a) I was born in the 50's and (b) I was 50!
It was really fun and we got totally into the experience. Believe it or not, the decorations at our table included a canister set that I have in my kitchen (from the 50's, was my Mom's). It was so cool!
Everyone in our room sang Happy Birthday to me, the waiter/cousin passed around a birthday card, and I got a cute little cupcake dessert with a candle. I even ran into someone who was there for my "party" later in the day and they wished me a Happy Birthday again. They signed the card "cousin" John and Jane and introduced themselves that way to me when we met later.
It was a great time (and they have a bar there, so I got libations with the meal too).