IU - 좋은 날 has some really nice vocabulary and grammar in the lyrics.

The first line "어쩜 이렇게 하늘은 더 파란 건지" helps me remember that 파란 is blue since 하늘 means sky. I used to always get 파란색 and 빨간색 mixed up!

Suho ft IU - Monday Thru Sunday is a great song for learning the days of the week.