I like certain pieces when played on the piano. My dad used to play them very, very often when I was a kid (probably a baby) and when I sit down near the piano and listen to them I become sort of sleepy. It's nice.

Rain at night is another one. But it normally has to be at night. If I hear it during the day I immediately assume that it is cloudy outside, and I don't normally like cloudy days. But yeah, night's are good. I sleep easier, even if it isn't real (nature sound tracks work just as well).