Golly, there is SO much, I wouldn't quite know where to begin. 
The first poem I ever set to music was my own, but shortly thereafter I discovered a collection of lyric poetry by James Joyce (1882-1941) called "Chamber Music" (1907).  It was his first publication of poetry, I believe, and for me it yielded a few good things.   
Check it out:  Chamber Music by James Joyce  Don't be put off by the simplicity of the poems; often it's better to set those than more complex works.