The Classical Music group put this one in my head today by mentioning the Merry Widow. I refuse to take responsibility for the humming, singing, and smiling! Then again, Lehar did write Land of Smiles as well. Here, then, is the Merry Widow Waltz.
First, we have an instrumental version from 1907, very close to when the original operetta was written.
youtube.com/watch?v=Uig1bseIjS…
Now, from Richard Tauber, with words in the original German. Lehar and Tauber worked so closely that it was like Novello and Hassall, only instead of writing the lyrics, Tauber sang them, and very beautifully, I might add. There are many other videos of him, including several with Lehar himself at the piano!