Josef Suk's Op.25, the Fantastic Scherzo -- This is my favorite piece of music at the moment. It's a solidly happy piece that Suk wrote not long before the death of his teacher Antonín Dvořák, and then his wife Otilie the next year. This is his Opus 25; his Opus 27 is the Asrael Symphony, named for the angel of death. In that context, I can't help but hear it as powerfully bittersweet, particularly since Dvořák had urged him to write lighter, happier music as a student.
I'm still looking for a recording of it myself, but here's a Youtube video in the meantime: