You will also frequently come across moments in songs where the composers themselves use the 9th as the melody note. Here's a simple example. Think of the song from 1930 'I'm Confessing That I Love You'. It begins with the words 'I'm confessin' that I love you. Tell me do you love me too?'
That word 'too' is the 9th of the chord in the harmony at that point. If the song is being played in the key of F (as it usually is), the chord is D7th (D F# A C) but the melody note is E.
You can hear the effect in your head, can't you?