Some poets became favorites of Lieder and art song composers. One place to find settings of a particular poem or poet is Index to Poetry In Music, in the Reference collection: ML128.S3 B69 2003.
The Lied and Art Song Texts Page has indexes by composer, poet, and title as well.
Many composers set "cycles" or groups of songs to poetry by one poet. Favorite German-language poets for cycles were Goethe, Heinrich Heine, and Wilhelm Müller. Use keyword searching to find CDs of music set to specific poets' works, e.g. "heine and compact and lieder or songs."