I agree with some others, sometimes it isn't a physical gift that tops my list either (though all gift items become part of my SM kit).
For the past 7 seasons, I've been a resident SM for a ballet company. Since my birthday is in November, for the past 6 seasons, my birthday has fallen on a tech or a performance. As a general rule, the dancers sing during Company Class for the birthday dancer du jour, but for my 30th - they went all out for me. During bows for our final afternoon tech, they got the Sound Engineer to play Happy Birthday over the house system, they all sang to me, and one of the principal men pulled me from my console and ran me out center stage, as Spot 1 picked me up. Everyone was applauding, so as he turned me across his body (typical ballet bow style for men & women) I took a deep curtsy and jete'd into the wing back to my console. I was flushed and thrilled at the same time (and I think I pulled something!).
To top it off, the show was Pirates of Penzance - The Ballet, and we had 4 live opera singers who sang along as audience members in box seats with the orchestra in "3rd person style" - quite a tasking job to say the least, especially if you've already performed the show and have sung it in your own 1st person voice. After bows on Opening Night (that same day), the quartet came to me backstage and sung "Hail, Les Reinhardt!" A cappella to me at my console (the Soprano had re-written the words to "Hail, Poetry!" for me). This just made me cry. I'd done a few shows with the Soprano before, and we had taken her to China on tour with us, so it seriously tugged at my heartstrings. She gave me a copy of her lyrics and it's something I treasure to this day.
And, on a non-birthday related note, last summer season I worked on my very first workshop. On closing, the Director of the New Works Festival came up to me to tell me that the director of my show had said great things about me. It's always great hearing that, but what was the best was when I went to say goodbye to the director. He said, "I am going to ask for you the next time I work here." That just floored me and filled me with so much joy that my chest nearly burst.
Sometimes, as we go along in our trade, we doubt ourselves. Perhaps we feel that our methods are out of date, or we're losing our touch, but to hear that, honestly and without provocation, really helps me to know that I'm on the right track. That is one of the best gifts ever.