How to Read a Poem : and Fall in Love with Poetry by These give you definitions, critical terms, overviews, and further references. Also, a great way to come up with search terms!
The New Princeton Encyclopedia of Poetry and Poetics by 
Dictionary of Poetic Terms by 
The Oxford Handbook of Modern and Contemporary American Poetry by The Library Catalog indexes books by poet as author, and anthologies by subject heading (do a keyword search). The poem may be in the Literature Online database (below); look also for an authoritative version via a reliable Web site.
