I agree with Mame and would add the original curtain call for Hello Dolly to that. They are admittedly essentially the same curtain call, but they are delightful in the extreme.
If one included 'One' from A Chorus Line, that would certainly be a candidate...the way the sole bows are worked into the number is brilliant.
Then there is 'Over Here' from 1974; after the traditional curtain call, the Andrews Sisters proceeded to perform a mini-greatest hits concert that the audience loved. I saw the show 5 times, and both sisters appeared in each performance, so I don't know what they did when one was absent. As enjoyable as the show was, that mini-concert was definitely the icing on the cake.
I did not see the revival of Lend Me A Tenor, so I don't know if they repeated the curtain call from the original production, in which the cast essentially performed a Cliff Notes version of the entire show in about 3 - 4 minutes.
Finally, I believe that -- regardless of what audiences ultimately think about the show -- Moulin Rouge is going to proceed close to the top of the list; The curtain call, which goes on forever, is deliriously joyous and as over the top as one would hope for.