It is the nature of poetry, real poetry anyway, to be spiritual to some extent.  That is simply because of the rhythm of well written poetry, regardless of the subject matter.  Some poets are better at writing spiritual poetry than others, of course.  Some that I recommend everyone read are:

• William Blake
• Kahlil Gibran (especially "The Prophet")
• Rumi
• Sri Aurobindo

Of course, much of the Bible, the plays of Shakespeare, and the books of Dante are poetry.

When reading poetry, it is always best to read out loud to get the proper vibrations from the rhythm of the poetry.