Vivaldi, "Winter " from The Four Seasons; the rising passage of six notes that is repeated thrice, one note higher each time, by a sweet violin floating over the harmony.
Mozart, "Andante" from Piano Concerto 21, the "Elvira Madigan" theme: after the piano melody builds up for the first time, there follows a descending violin (I think it's a violin) passage of 7 notes. It is immediately repeated and picked up by some other instrument, and recurs several times afterwards.
Music really doesn't translate well into text. But I have a small pause of happiness inside whenever I hear one of those passages. It's the same with a few math theorems, and a couple of lines of poetry, a couple of sets and the lighting and movement of the actors or dancers on stage for just that moment, and a small number of paintings, and some views out a familiar window - when you encounter those tiny bits of them, there's a small quiet ping! and you sigh a little inside, and you continue on with a lighter mind.